If a recent problem was, as I recall, downgrading of civil standards and generally, of intelligent discourse, I cannot see how downward karma capping can help. It will only encourage trolls and flamers.
I don't think trolls and flamers care about karma. As long as their individual posts get low enough to be out of sight, whether they're at -8 or -50 doesn't matter. Presumably users will still get banned for the same extent of trolling and flaming.
