I have to agree with most of the posts about the lesbian side being the young girls in schools having sex because there were no males around, so of course, it was innocent.
There is one other factor though that I feel needs to be looked at. It is the factor that most people fear what they don't understand. Lets face facts, most of us have been raised in the Puritan mindset that is very straight laced and very narrow minded when it comes to sex. If it is not male and female, then it is morally wrong. The Puritans refused to accept the fact that there were then and have always been people with different sexual persuasions, especially homosexual. It is an established fact that in general 1 in every 10 people in the world is homosexual in some fashion.
If you want to freak out a real homophobian, tell him that fact, then advise him that if he or she knows 9 straight people, they are it.
I know that it took me many years to get to the point of being open enough to be able to learn about and accept alternate life styles. This was a great thing for both my wife (who learned this first) and myself, when our oldest daughter came out to us that she was lesbian. This was something that we had suspected for a couple of years, but did not want to confront her about until she decided for herself.
Again, I feel that fear of the unknown is the major problem with why some things like young girls with young girls is acceptable, while other lifestyles are not.