I think there are two core drivers that are behind most of the negativity. The first is incompetence, and the second is something close to malice.
For the incompetent commenter:
1) Blind criticism is cheaper than thoughtful feedback.
2) It makes the giver feel superior to the target of their criticism.
3) Cue the dopamine reward. Rinse and repeat.
For the malicious commenter:
1) They have a vested interest in discrediting the target. (Other accelerators -> YC, Other markets -> Silicon Valley, Competitors -> You, etc).
2) Negativity serves these interests.
3) Cue the (perceived) economic reward. Rinse and repeat.
Between all this, you'll find the occasional piece of genuinely thoughtful feedback. It's worth looking for, but you'll need to develop a rather thick skin if you want to wade through the muck and mire to find it.
For the incompetent commenter:
1) Blind criticism is cheaper than thoughtful feedback. 2) It makes the giver feel superior to the target of their criticism. 3) Cue the dopamine reward. Rinse and repeat.
For the malicious commenter:
1) They have a vested interest in discrediting the target. (Other accelerators -> YC, Other markets -> Silicon Valley, Competitors -> You, etc). 2) Negativity serves these interests. 3) Cue the (perceived) economic reward. Rinse and repeat.
Between all this, you'll find the occasional piece of genuinely thoughtful feedback. It's worth looking for, but you'll need to develop a rather thick skin if you want to wade through the muck and mire to find it.