I partially agree with you. Right now the people most likely to switch are going to be the people who have no home. The crackdown has started, but it's pretty early. The people kicked, or leaving at this point are not the ones you want to be the early founders of your social network. Remember, the first users set the tone for the community.
Your last point isn’t a truism as networks approach global scale. Early users of Facebook and Twitter have not set the tone - they may have influenced it, but particularly in Facebooks cause, any such influence has been largely diluted away.
