Do you seriously think saying no to a child means they'll do it anyway and not talk about it so you never say no?
Can't say that makes much sense to me. Having been involved with "problem" children and thus child psychologists they all say setting rules is important. Obviously talking to children is too, as well as making sure that they can talk to you about anything and that there's a way to resolve things if they break the rules.
Personally I find getting kids to use computers is easy, as is getting them to use social media in the way of "chat" in games is also easy. What's harder is getting them to do their home work, tidy their rooms etc. Pretty much the same things as when I was a child in fact.
I find it hard to see any advantages to getting children heavily involved in social media at a young age as it's not exactly a hard to learn "skill". On the other hand the time when they can play with abandon, pretend to be a dragon, collect lady birds in the garden is relatively short and won't come again.