There is a very clear difference between sexual abuse of minors and the ability to communicate. One is bad regardless of how you frame it, the other is dependent on the respective medium and how it is moderated.

Giving a 15 y.o. a platform to discuss stuff with peers, even if there are people out there who might try to groom them, is a good thing. The groomers are the ones that have to be reigned in, not the teens.