What is 'the norm'?
Can you imagine watching a nature program on the BBC or Discovery and see the commentator commenting on two adult lions are walking around each other, checking each other out as part of their mating dance?
That is not the norm! If gays and lesbians can be considered the norm, then the human race is on a fast track to extinction!!
How can you have kids, who are highly impressionable to be in an environment where people are all either gay or lesbian? They'd think that, in deed, is the norm. Can you imagine the psychological influence on kids who are constantly bombarded with ideas that being gay and lesbian is part of 'the norm'?
The teachers' job is to educate children. He/She needs to identify what is 'the norm' to the kids but also point out that some men find that they're attracted to men and some women are attracted to women - but that is not 'the norm'. If the kids want to experiement with their sexuality, that's their business, but they have to have a reference point. If they're surrounded by gays and lesbian, then a man with a woman in a relationship is considered 'abnormal'!! What kind of a society would we have then??