That's not the point.
That's exactly the point for all the reasons you list in your post. I just come right out and say it. A 'homosexual' male cannot be trusted in the company of boys. He must be considered a child molester. Likewise a 'homosexual' woman cannot be trusted in the company of girls. She must be considered a child molester
That's fine - if you also believe that every woman must be considered a child molester and so cannot be trusted in the company of boys. I doubt you'd say that.
I would agree there are too many homos who would take advantage of this type of situation to gain access to fresh meat (similar to what they have done in the Catholic priesthood). But then, if women were allowed to mentor boys (or men allowed to mentor girls), you'd have the same issues - predators looking for fresh victims.