This is re-posted from last year.
One of the ways to read Plato's Gorgias is as an argument that the practice of philosophy requires the virtue of temperance (sophrosyne, self-control), and vice versa. This contrasts with rhetoric and sophistry, which have no such connection. In fact, the rhetors in the Gorgias end up explicitly affirming a number of things that are inconsistent with the virtue of temperance. The reason for this has to do with the distinction between what seems good and what is really good.
Gorgias claims that rhetoric is valuable because it is concerned with speeches that persuade, without educating, on matters of right and wrong in the city; as Socrates notes, this means that rhetoric deals with what seems good rather than what is really good. This is affirmed when Polus argues that orators are powerful because they do what they like (i.e., what seems good to them). Socrates, however, denies that what people like (i.e., what seems good to them) is what they want (i.e., real good), although, of course, since he likes provoking Polus, he states it in the most paradoxical way he can find. For instance, Socrates claims that people who do wrong and are never punished for it are to be pitied, while being wrongly punished is always a happier life than doing anything wrong; Polus will be boggled at this kind of view, in which someone could suffer terribly and have a happier life than someone who gets everything they like. Callicles in turn argues that success, the good life, the life worth having, consists of desiring as much as possible and having the phronesis (intelligence) and andreia (manliness or courage) to achieve your desires, and denies that restraining your ambitions when you could achieve them is anything but either weakness or stupidity. Socrates will argue that all of these claims are incoherent.
But more than this, all of this argument, while about self-control, is also about philosophy. This is actually made clear in multiple ways. Early on, in the discussion with Gorgias, Socrates says that he hopes Gorgias is a man like himself: someone who would prefer to be refuted than to win an argument. The claim here is entirely analogous to Socrates' later claims about punishment, because both refutation and punishment are kinds of correction. Winning an argument is a matter of appearing good; but being right is a matter of real good. Not being punished is a matter of appearing good; being just is a matter of real good. In order to be the philosophical kind of person, rather than the kind of person we later learn (despite Gorgias' facile claims otherwise) the rhetors are, you must be willing to make a distinction between merely apparent good and real good. The oratorical conception of success is concerned with winning the argument, getting away with it; the philosophical, with improving the argument, improving oneself.
It's more than just a matter of aims, though. Socrates' argument against Callicles that the good life needs self-control doubles as an argument that the good life needs philosophy. (It is one of the standard marks of Plato's philosophical brilliance that he can make an argument about one subject also at the same an argument about another subject.) Socrates argues that the good and the pleasant (i.e., what seems good because it satisfies desire) can't collapse into each other. Callicles' view that we should desire as much as possible and satisfy those desires in neverending progress requires exactly this kind of collapse. But if we hold this view, we start getting very weird results: we should itch as much as possible, letting our desire to scratch grow as large as possible, in order to maximize the pleasure of scratching; soldiers should let fear, i.e., our desire to run away, grow as big as possible and then have the manliness/courage to satisfy that desire. Callicles tries to get out of this by saying there are better and worse pleasures, but this just breaks his argument against self-control: if some pleasures are better than others, we should sometimes control ourselves so that we get the better pleasures rather than the worse pleasures. Good needs to be discovered and accommodated; it cannot be imposed by force of will.
If real good and apparent good can't be collapsed into each other, though, then we have to reflect seriously about what real good is -- which is philosophy. Thus if the good life requires self-control, as Socrates argues, the good life requires philosophy.
If this is the case, though, it applies to reasoning as much as it does to anything else in life. Winning an argument is merely seeming to be good. Rhetoric may be able to give you that appearance. But the good of reasoning does not boil down to the appearance of winning the argument, however nice that might be; the good of reasoning is having a good argument that gets you something true, and what counts as that good must be discovered. Philosophical reasoning is temperate reasoning, in which you control and restrain yourself in order to find real good in reasoning rather than merely apparent good. Someone who falls back on mere rhetoric is someone who has committed himself to 'might-makes-right' in rational matters. There is a kind of very general moral realism about reasoning implicit in philosophy itself; if you reject the idea that good in reasoning is independent of our preferences, then in Socratic terms you are no philosopher at all: you are a sophist.
Note that the moderation here is not one of tone. Plato's Socrates argues respectfully with those who argue respectfully, but vehemently and polemically against those who argue vehemently and polemically. But Plato's Socrates is also quite clearly put forward as someone who insists that there is a real good of reasoning, and that it is discovered and not imposed by force of will. Because of that, we have to restrain ourselves, not running after merely apparent good but seeking that real good. That is philosophy.