Bah, just avoid pub servers like the plague and you'll be fine. I still enjoy it very much because I tend to avoid the servers where these kids go to, and frankly, I couldn't care less about TF2 being F2P. Sure, we get tons of idiot kids coming in acting retarded, but we also get new competent players too. If the game itself is free, there's no loss in trying it out, right?
I'm pretty sure most of these 12 year olds won't stay permanently, since they'll be off the game like the plague once their parents find out what they've been doing with their money.
Overall, yeah, I'm not too fond of TF2 becoming F2P mainly due to the wave of hackers and 12 year olds, but even then that wave will calm down in a week or so once the hackers get banned and the 12 year olds grow tired. Oh, they will still crop up, but once the storm has cooled down, it will definitely not be as common.