Nothing against communicating via Facebook, if that is your thing. But it is definitely not childish to not communicate via Facebook. Boycott is too strong, perhaps, but if you simply see no use for it.

Personally I am just old fashioned in that way, I still run my own email server. I don't feel too happy about my communications belonging to some mega corporation.

Also, I don't like having to log in to FB to get my messages, and in turn to be trackable by all the sites that partner with FB.

That's just my reasons - but I don't boycott it. If somebody messages me on FB, I usually reply. I just don't initiate communication on FB.