Not to put too fine a point on it, but some people actually do choose mates with some desire to find one with a complementary, functioning reproductive system for the purpose of using those reproductive systems with each other to produce zygotes that grow into children. Not everybody, of course, but substantial numbers of people want to do this, perhaps even the majority. It would be difficult to convince me that this desire, when present, is simply a prejudice that will fade as society changes, unless it starts being like Brave New World, in which case, the technology could probably be applied to making a John Varley world of complete and reversible sex-changes. That, however, is quite some time off, if it ever happens.
I'm not monogamous, so this isn't really a limitation for me. But, currently, mononormativity is strong, and in that context, telling a "squeamish" male that he should give up the chance of having children with his DNA, except perhaps if he can afford a surrogate, doesn't seem all that OK. In fact, it seems to me officious enough to compete with telling someone they have to be their birth gender for the rest of their lives. If people did it strongly enough, it might become associated with one or two suicides as well.
