I agree regarding being exposed to new ideas, but turning on "show dead" has given me some doubt. Plenty of regular comments get flagged and killed, e.g. this [1] comment that I vouched for. I can only assume, but it feels like people are feeling attacked because they enjoy the circlejerk and feel they must censor this comment that call them out.

[1] https://news.ycombinator.com/item?id=23175556