I guess dumb luck keeps me from encountering a normal amount of undesirable behavior, while agreeing that folding comments isn't likely to have been anyone's priority. I do see isolated memeoization, flames, etc. but it's not really a characteristic of "core contributors" unlike is more typical of internet communities.

For what it's worth, if indeed PG didn't consider thread folding interesting, I cannot say that I blame him since it is that way for me. The feeling that scrolling through a page to find some comment feels like a bother means that it actually is a bother and not worthy of the effort. Collapsible threads making it less effort to rebut won't increase the quality of my comments...on average, it will probably reduce them. YMMV.