I can see what you mean.
But I still think that, IF the parents went through it themselves, that's even more reason not wanting it to happen to somebody else, especially your kids. (this sounds to me like a "I went through it, so now it's somebody else's turn", pretty egoistical I think)

The mixed race anology is not really correct here I believe. Though I don't doubt that this created a lot of trouble in the past, and I certainly don't want to belittle it, this is something entirely different and thus an entirely different discussion. Because look at it how you like, you can't really say that being gay is being normal, how liberal minded you may be. Don't get me wrong, I don't mean to say it's a bad thing, just not normal.
The normal way of going about this is man + woman = child, not man + man or woman + woman. Something just doesn't add up there.

I'm sure mixed race couples had a LOT of difficulties in the past (and maybe even now still), but basically they still were about a man and a woman loving each other and having kids. I see nothing wrong with that. All the right ingredients are there to create a healthy stable family for the kid to grow up in. With gay people it would always be like there's too much of the one thing and nothing of the other.

Also, I don't think it really matters where kids get their ideas to be cruel to other kids. (be it teacher, parents, the wrong kind of friends,...) because I'm pretty sure you also don't care when you're the kid getting picked upon, that's all.