I missed some of the earlier threads and didn't want to reignite them. I feel more comfortable replying to PhilGoetz's comment since it's only from two days ago.
One problem that I didn't see anyone discuss is that this feature is likely to drive away new users. This policy discourages interaction with new users because unpopular comments overlap significantly with comments from new users. By discouraging commenters from responding to the low quality posts of new users, we disincentivize the picking of low hanging fruit, which is the opposite of what we should be doing. In addition, by doling out karma penalties at a set level rather than as a fraction of total accumulated karma, new users face much heavier fees than regular users, which will also result in increased insularity.
In light of recent (and potential) events, I wanted to start a discussion here about a certain method of handling conflicts on this site's discussion threads, and hopefully form a consensus on when to use the measure described in the title. Even if the discussion has no impact on site policy ("executive veto"), I hope administrators will at least clarify when such a measure will be used, and for what reason.
I also don't want to taint or "anchor" the discussion by offering hypothetical situations or arguments for one position or another. Rather, I simply want to ask: Under what conditions should a specific poster, "Alice" be prohibited from replying directly to the arguments in a post/comment made by another poster, "Bob"? (Note: this is referring specifically to replies to ideas and arguments Bob has advanced, not general comments about Bob the person, which should probably go under much closer scrutiny because of the risk of incivility.)
Please offer your ideas and thoughts here on when this measure should be used.