In every practical field, human beings have a craving for panaceas and a taste for nostrums; it satisfies both our desire to know and our desire to be in the know. Ethics is not any different in this respect; there are many ethical quackeries, and an endless number of people falling for ethical quackery in the attempt to have a simple answer. 'At least I'm not a hypocrite' is a perennial favorite, due to giving all the benefits of hypocrisy while passive-aggressively holding oneself to a minimal standard and putting everyone else on the defensive. There is a never-ending task in having to explain, as patiently as possible, to yet another person that 'consent' is not on its own a serious standard for ethical matters because it is met even by a bar brawl taken outside or a murder-suicide pact. And the form of ethical quackery that currently seems popular is boiling all of ethics down to kindness, as summed up in the advertising slogans (today, even ethical scams have them) Just Be Kind or Kindness Is Everything.
It's a clever scam because kindness is obviously good in its own way -- who is going to go around saying that kindness is bad? -- and because it tells people what they want to hear. There are endless numbers of reasons why kindness, important as it is, is nonetheless a secondary, and not a primary element of ethics, that it is a seal of excellence for an already substantive goodness and not the substantive goodness itself. We could go through Frederick Douglass's argument showing that kindness among slave owners actually made things worse for slaves, gilding the chain, or Philip Hallie's argument in "From Cruelty to Goodness" that kindness, despite superficial appearances, is not even the right kind of thing to nullify and oppose cruelty. These would be all correct. But they wouldn't deal with the essential problem, which is that people have an incentive to ignore such arguments.
'Kindness', etymologically, is the kind of affectionate good will you have toward family, and as used in modern English the word always concerns sympathy -- sympathetic generosity, sympathetic forbearance, warmth indicative of sympathy. There are all sorts of reasons why someone would want this to be the moral standard in everything that signal that it can't be the moral standard in everything.
(1) Kindness is mostly a matter of attitude, and thus can easily be faked. There is no particular form of action that is especially associated with kindness, because it's about the way you do things; when we say that someone is kind, we are saying that it is the sort of thing a kind person might do, done in the way a kind person might do it, and we see no reason why someone should not get credit for having done it in the right spirit rather than passive-aggressively or in a spirit of hypocrisy. This means that anything that involves any kind of benefit to anyone can be spun as kindness, and you can often convince people to give you the benefit of the doubt for it, because even if it went very bad, they will usually not have definite proof that your intentions weren't kind. Kind intentions can easily be faked because, while we sometimes have direct evidence of them (e.g., people seeming kind even at harm to themselves) and sometimes have indirect evidence of them (e.g., people doing things that seem kind consistently across time), most of the time we are just assuming that it was done with kind intentions. There are lots of good reasons why we do this, but it's a red flag when what is being proposed as a fundamental moral standard is a standard that can easily be faked.
(2) Kindness is mostly a matter of attitude, and thus can easily be ignored. On the other side, the fact that our inference that other people are being kind is only probable means that if you really want to be stubborn, you can treat someone as being unkind regardless of the evidence -- after all, we know they could always be faking. So if you're offended at what someone has done, you can easily brush off any attempt on their part to try to assure you that they meant it kindly. And what's more, since you can stubbornly treat anyone who offends you as being unkind, just by not giving them the benefit of the doubt, if you take kindness as the moral standard, you can treat their failure to accommodate you not just as a deficiency or error in moral action but as the gravest moral failing. Another warning sign: a proposed fundamental standard that can be used as a wax nose.
(3) Even when sincere, kindness is not a high standard. Being kind can be difficult, if it's a matter of being kind in a situation that is already morally difficult; this is why kindness can be seen as a sort of seal of excellence. But this is not true of kindness in general. Kindness has no particular action associated with it; being about the way you do things, it can cover all sorts of things. And because it is a matter of attitude, you can be kind even when you are obviously not really doing anything but having the right attitude. You can face a moral problem, make no serious effort to solve the problem, and still be kind. (This is precisely one of the things noted by both Douglass and Hallie.) And kindness often has immediate reward for yourself; people often talk about how doing something kind made them feel good. Another warning sign: a proposed fundamental standard that you can usually fulfill just by doing some minor token action in the right frame of mind, feeling good about yourself.
(4) If you are kind, people owe you. Kindness, to the extent that we can recognize it, has to be repaid with gratitude; failure to repay it is ingratitude. This is why doing something that could be regarded as kind is one of the standard ways confidence games are run. People are not easily persuaded just to give up things, so a con artist has to find a way to make them feel that they have to do it, that somehow they can't not do it. So a con game is usually ethical sophistry: I have done something obviously good for you, now you have to do something good for me, and I have arranged the terms so that it was easy for me to do that good thing but it's morally bad for you not to do the difficult thing I want you to do. So a con artist will trust you with secrets in order to get you to tell secrets -- after all, he gave you his trust, how can you not give him yours? Or he will do a purely symbolic goodness for you, out of the blue and as a pleasant surprise, in order to get you to do something substantial. One of the reasons ethics is a serious matter is that ethics is regularly used to manipulate people. It's not what it is for, to be sure, just as logic is not for the purpose of a sophist leading you to any conclusion he wants. But if someone wants to manipulate you, they will use something to do it that has an authority you recognize, whether that is logical principle or practical necessity or ethical obligation. Thus it is another red flag for quackery whenever you have a proposed fundamental standard that gives a significant set of advantages to the manipulative.
I could go on, but you get the idea.
In many ways, 'Be Kind' and 'Kindness Is Everything' are like 'Spiritual But Not Religious'; you could make perfect sense of them in a narrow area of human life, but 'Spiritual But Not Religious' usually means you are trying to have the benefits of being spiritual without the discipline and social burden that spirituality requires, and 'Kindness Is Everything' is an attempt to have the benefits of being moral without the hard-to-build, difficult-to-plan moral context that kindness really presupposes. (A recent "Pearls Before Swine" comic, I think, inadvertently gives away that parallel.) If you are boiling it all down to kindness, what that really means is that your standards are too low; you are jumping to the end, to a crowning virtue, and pretending that you don't need any of the completely different virtues that kindness is supposed to crown.
Of course, even ethical quackery in the Internet Age has to have a marketing website (as vague and inoffensive in patter as possible) and merchandising (and more merchandising). It's not for-profit, but fundraising for ethical and purportedly ethical causes is a natural context for ethical quackery. And I've no doubt that it is often quite sincere. Quackery of any kind only has sustainable success because it gives people something that is genuinely recognizable as good; that it is a good feeling or a good self-image doesn't change the fact that you can actually get something from it. And if just a small number of people are convinced that the good is substantial, you have real converts who will sincerely work to spread it. That's how health fads spread, for instance -- the kind that spread are always the kind that are easy but can deliver at least some apparent good for some small group of people by making them feel like they are making progress because of the fad. And it's how ethical fads spread, as well. Not all fads are bad or even wrong -- usually the only problem with them is that people are not recognizing their limits. But sometimes a fad is dangerous because it will look good to people while replacing things that are better. Kindness is a good thing indeed, but it presupposes a lot that you can't just will into existence. Kindness is a flourish that makes good things better, that takes other moral things and morally enriches them; it does not stand on its own and cannot substitute for these other things. You are better off recognizing that kindness is not enough, and that it certainly is not everything.