"[...] why is it unfair that parents (whose interest is in seeing their kids marry and produce the next generation) would be worried about their kids being told that homosexuality was "perfectly normal"[...]"
One would hope, perhaps unrealisticly, that the interest of these parents would be for their children to be happy instead of being 'as much as the rest of the population as possible so as to not stand out.' Especially in a place like /. where abberation from the norm is probably the norm, I think your point of view is odd :).
I see no reason why gay parents are worse than straight parents and I personally know children being raised by gay people around me. These kids aren't gay themselves and the role-model doesn't seem to influence that 'position' in the least. If having grand-children (even with their own DNA) is the biggest interest parents have, their children being gay does not have to stand in the way so that argument is out the window. The argument that gay parenting or 'gay propaganda' begets gay children is unfounded(*) and sounds much like arguments brought forward by racists against mixed-race mariages or TV shows showing such mixed race bonds. Oh. Wait. Isn't that one of the last big taboos on US TV? :D.
To answer your final question
"Why, if homosexuality is "fixed", are pro-gay groups working so hard to get books promoting their lifestyle into kindergartens if not that they're trying to propagandize kids the same way and pick up some numbers?"
perhaps superfluously: for the same reason the best way to beat racim is for children of different races to play together so that when they grow up, differences in color of skin and other racial characteristics are a natural thing to them. It doesn't turn someone from one race to another (with the odd exception, here and there ;), but it makes these "impressionable minds" accept more easily that there is more than one way to do things so they won't discriminate against those who are different. Perhaps nerds and geeks should start such propaganda in pre-schools as well... :P
(*)If you know of independant, verifyible scientific studies that support the 'gay surroundings turn you gay' idea, please point them out so I can read up.