[joe_the_user]

Well, one thing is the mere act of commenting on X tends to make one more committed to X. The process of becoming what you say is accelerated by people posting links, memes, cut-and-paste-me's and so-forth.

A person may not fully believe meme X but they may "find it interesting", may want to "rattle people's chains a bit". Then someone else launches a full attack on meme X and the person feels, attacked, and defends, attacks the other person and so-forth. Polarization is powerful and well-documented dynamic on the net.