Pejorative terms are a big, fashionable topic in philosophy of language. There's a lot of work done on them. (The IEP article on pejorative language summarizes some of the main ideas in a small part of the field.) Most of the work is not particularly good (a common problem with fashionable topics in philosophy), and I think is sometimes seriously misleading. Obvious points are missed, obvious problems overlooked, a lot of dead-end clutter based on controvertible assumptions. But my own thought on the topic has mostly been recognizing obvious problems with other people's arguments; I've never really thought through the topic in any systematic way. I'm certainly not going to be able to do that in a post, but blogging is a fairly handy way of beginning to gather your thoughts together on a topic. So some rough and not-fully-formed thoughts about issues with regard to pejorative terms.
(1) The big, fashionable subtopic in this topic is the slur. I suspect a lot of people do work on the subject because they hope that looking at the linguistic issues of slurs will help in thinking through political, social, and ethical problems. It is a subtopic, and I think not everyone publishing on the subject really grasps this. Not all pejorative terms are slurs. If I call you a doofus, 'doofus' is a pejorative term; the use, however, is probably affectionate, and affectionate pejoratives are not slurs. Likewise, pejorative terms can be insulting without being slurs. You cannot tell that something is a slur simply by looking at the word, or even always by looking at its use in its immediate context. 'Stupid' is pejorative; it can be insulting, and often is; it is not generally a slur, since in English it functions as a generic and general purpose insult. In addition, while there are terms that are only ever pejoratives, any term that can apply to someone can be used pejoratively.
A pejorative term becomes a slur in a context in which it is known that it could harm a person's reputation by specifically classifying them. 'Yankee' (or 'Yank') is a pejorative term. In Britain it might be a pejorative term for Americans; it may sometimes be a genuine insult, but it will not generally be a slur when actually applied to Americans. (Perhaps it would be a slur to apply it to an Englishman; I don't know.) In parts of New England it is a pejorative term some New Englanders use for themselves -- an affectionate pejorative. In Texas, 'Yankee' is a slur for New Englanders, and a fairly significant one; do not walk into a Texas bar and call someone a Yankee, because you might get a fist to your face. This is because of different background cultures. A New Englander calling himself or his forefathers Yankees is not assaulting his or their reputations, but probably only using the pejorative form to emphasize something that the pejorative term does, in fact, make it easier to emphasize -- trader shrewdness or boldness, for instance. It's a bit like calling a good friend a con man; you probably aren't actually trying to ruin his reputation, but instead emphasizing his cleverness, which the pejorative phrase 'con man' helps you emphasize. (Use of pejoratives as means of emphasis is quite common, in fact.) In Texas, however, there is a long, not-entirely-friendly history with New Englanders that has led the term to being rude at best and, in the right context, viciously insulting; it is an attack on a person's character and integrity, not the worst possible way to do it, but not a very mild way to do it, either.
This is true of pejoratives and slurs generally; all slurs are pejorative terms, but it's neither their extension nor their immediate use that makes them slurs, but a context in which the pejorative term becomes an attempt to harm people by way of their reputation. The most common (although still controversial) way of explaining slurs is the double-meaning or mixed expressive account: 'Norgie', for instance, is a pejorative that refers to Norwegians (its extensional or truth-conditional meaning); it expresses contempt or disapproval (its expressive or use-conditional meaning). This kind of account inevitably is much more complicated than it looks, due to the fact that pejorative terms are not always applied to their extension (like someone in Texas calling a Texan a Yankee, given that in Texas it only refers to New Englanders, especially New Yorkers), which is sometimes the whole point, and to the fact that any pejorative term (and this is true even of terms that are usually slurs) can in some contexts be used in ways that don't actually express any contempt or disapproval at all. But more fundamentally, it's clear that any such account can at best identify pejorative terms, not pejorative terms that are specifically being used as slurs.
(2) A pejorative term is a term; a slur is something classifiable for social reasons as an attack.
(3) If this is the case, then a common view of slurs -- that they have 'expressive autonomy' -- is simply wrong. Expressive autonomy, applied to slurs, is used to suggest that the slur has its full derogatory force regardless of the attitude of the person who actually uses them. A slur is a slur always. This is not plausible. First, because it does in fact matter who the speaker is; only a child thinks there's never a difference in derogatory force between when a racist uses a pejorative term about a race and when someone from that race uses the same term. Second, because slurs are actions expressive of attack, and therefore a term that is a slur in one context might not be in another.
(4) While it's common to use the word 'expressive', we have to be careful. Just as musical expressiveness cannot be reduced to actual expression, so the 'expressiveness' of a pejorative is not necessarily what someone is actually intending to express. The history matters. This is the hardest part of an account of slurs; they have to be defined not in terms of immediate context (which just gives us insults that may or may not be slurs) nor in terms of universal language contexts (which just gives us pejoratives) but in a middle context, a stable social context with a history.
(5) It is history that explains why some slurs are worse than others. On the other hand, some people have argued that a slur indicates an allegiance to a particular unified perspective; this is obviously going too far in the other direction, since it makes the history over-specify how the slur is to be understood.
(6) If you step away from slurs and look at all the accounts of pejorative terms in general, it's pretty obvious that people are just picking out some feature of general language use (tone, implicature, presupposition, or what have you) and trying to stuff pejoratives into an explanation based on that. But we should, I think, take seriously that pejoration is (1) an integral part of language in general and (2) a distinct part of language use in its own right. One reason for thinking this is that some terms seem to be able to be used pejoratively or not regardless of their tone, implicature, presupposition, etc.
There's another aspect of language that seems similar: polite compliment. Together with pejoration, compliments make up part of the etiquette of language, in a broad sense of the word 'etiquette'. Etiquette is a part of language. This is very obvious in languages like Vietnamese or Urdu or Japanese, where you can't speak correctly at all without recognizing the appropriate etiquette-situation, but it is true even in very etiquette-informal languages like English. Speaking derogatorily about people is just one of the things language is for; it's one of the things contributing directly to the meaning of words. (Fortunately for us, not doing so is also one of the things language is for.)