While I am not entirely opposed to having homosexuality in the game, it would be nice if it came with a little on/off button, so that those of us making small fortress, where babies are important, wouldn't suffer for it. Also, so that those people who would rather not be confronted with it, won't be either.
I have heard some arguments about how it is "normal", which it is, and how it is practised in ancient cultures as well, which it was. But we are dealing with dwarves here, NOT humans, keep that in mind. A fictive race living underground and fighting demons aren't exactly realistic either and this fictive race can be anyway we want it to. If we say dwarves can't be homosexual, you can't exactly disprove it with examples from our own culture.
I am not sure we want to emulate our own society too much in every regard with everything that entails. Would you add non-consensual sex as well, just because it is done in our own society and have been done, for millenia? What about prostetution, child marriage and so on? No, I did not think so.
tl:dr I have no problem with it being added if I can turn it off. Too much realism isn't necesarily a good thing.