I don’t think internet causes OTD, I think being unhappy and in pain, usually having been traumatized (specifically, abused), causes OTD. I agree that those who are suffering escape to places which are harmful, and that can be the nail in the coffin, so to speak, but the primary cause is pain.
This might not be the case in more permissive homes where internet is allowed, and children exposed to the idea that all types of ideologies are equal ch”v. This has been proposed by Rabbi Dr. Berman.
http://www.theyeshivaworld.com/coffeeroom/topic/sunglasses-assur/page/2#post-580900