More a speculative thought, but if those who do pay attention to negative feedback no longer see any, they may not take that into consideration when they put things up.

Say someone put up a post, saw no backlash on the front end, but then comes to look at the responses and sees a cesspit of hate. That's hardly going to soften any mental harms it might otherwise impose.

Another thought here is messing about with such things, particularly in making them a default behavior, could disrupt comms where there is a strong voting aspect to it. The 'am I the asshole' type place that, despite the usual attempt to have them adjudicated by some nuanced comment system, inevitably end up using votes as a agree/disagree dynamic.