Anything to fight the "don't read the comments" attitude people have adopted when using the internet. By requiring a tangible investment in your comment, it helps ensure people will make more succinct threads and spend less time trolling.
Trolls may well be willing to pay to play, and corporations definitely will, but it seems to me that it might accidentally dampen attempts at casual or in-depth conversation. The fewer people who participate in a community, or become invested in it through interacting with other users, the quicker it'll die.
