That article Glowcat posted is a good one. While, unfortunately, it doesn't have a concrete answer as I was hoping for, it does reaffirm the opinion I already had that there doesn't really have to be one.
Gender roles are a very, very grey area for me. As a concept, I don't really have a tremendous problem with them, but there are a huge number of caveats that go with that statement. Current western society, by and large, has a conception of them that is unacceptable to me, as I see it. The absolute most important thing for an acceptable system of gender roles is that they must be flexible, and fuzzily defined. You can't have people telling others that their identity is "wrong", and you can't have a particular characteristic that is absolutely, 100% assigned to one gender. The roles as they exist are also unfair; generally, women find themselves in subservient roles, and while women have a relatively fuzzy enforcement of their gender roles, the acceptable roles are very narrow, and there are still some things that it's just plain expected will be true of any woman. Men, while typically winding up in relative positions of power and with a broad range of roles to assume, have a very sharp enforcement of the roles they are allowed, meaning that a man who steps out of what's acceptable receives very strong and clear criticism (I could write an essay on the problems this asymmetry causes when trying to discuss sexism).
To address one particular complaint, I don't object to children being assigned to a gender group as an unfair imposition by parents and, on a larger scale, society, on the child's ability to develop and grow freely. Parents have to structure a child's identity as the child grows to fill it. That's just part of being a parent. It's why I don't object to religious teachings, family recipes, holidays spent with the extended family, children moving with their parents to new cities, and so on. The objections start only when parents refuse to accept the child's input; it needs to be a dialogue in which the child grows, and you have to be willing to accept that perhaps your child will want to make their own decisions (indeed, the ultimate goal of parenting is to prepare the child to do exactly that).
At any rate, I feel like the absolute most crucial thing to remember is that a person can never be told that they are wrong about their identity (disclaimer: not addressing corner cases here, I guess, just try not to be a douchebag). They know it better than anybody else does. If you start from the position that there is a Right Answer and everything else is a Wrong Answer, you're never going to learn anything about anyone else - you'll just learn slightly more effective ways to arrange the stereotypes you started with.
Regarding MSH's position - I actually share it, and it's for exactly the same reason I agree that that article Glowcat linked is a good one that I think it's defensible. If part of your sexual identity, however you arrived at it, includes some particular turn-off, who the hell is anyone else to tell you that you're wrong for having it? We're not talking about some logically arrived-at conclusion - sexual identities are tremendously complicated amalgams of experience and inheritance, every bit as ineffable as, "I am a woman." And remember, you don't need a reason to revoke consent. At best, it's polite to give one.
EDIT: I want to clarify what I said about children making decisions. It's not exactly a good choice of terminology, but I want to leave it for posterity and to avoid looking like a weasel if anybody replies to it while I'm typing this. In retrospect, I should have kept to the growth terminology and described the child developing an identity that doesn't conform to the confines of the structure provided by the parent. I do know that there's a hell of a lot here that isn't deliberate choice - I'm just tired and falling into old vocabulary patterns out of a habit I really need to grow out of.