'Imposing' is a strong word. If that is happening, I would expect incidents like the following:

"Little Johnnie is called to the head teacher's office. She says she has something serious to say to him. She understands that he has been telling the other kids that he is not gay and that he is attracted to girls. The head teacher says he must stop saying such things. We are all gay. It is wrong for him to be attracted to the opposite sex. He should be attracted to members of the same sex."

Now, I do not think things like that are happening in schools. I could be wrong, but I would need some good evidence of that before I would believe it.

This is not to say that I think all aspects of current sex education are good. Far from it. Kids need much more honest information about sex, its pleasures as well as its more negative aspects. They should be told in a straightforward and non-judgmental way about the full gamut of sexual variations (including bisexuality, which tends to get not nearly enough attention). And they should also be told about minor attraction, the positives as well as the negatives. Of course, this is a very idealistic wish list. If teachers actually did this in the present climate, they'd all be fired!