Clearly there have been users whose posts have been overwhelmingly bad. Downvoting a bad post when it's posted isn't a problem. The problem we've seen is when someone decides to carpet-bomb all of a user's past posts, indiscriminately, in order to make some kind of "statement" against that user. Please read reference 1: History now influences voting. I should note that tye's changes to address the problem don't work 100%, as we still get users who mass-downvote another user, deciding to just suck up the negative consequences from tye's changes. tye also said "administrative intervention sucks" but I have no problem manually intervening to address the corner cases.

If all my posts are garbage that could be considered dangerous or detrimental to ones sanity/task/career, wouldn't each merit a legitimate downvote? Surely it's my fault that they all suck?

Downvote them as they happen, if they're bad. Don't decide "I need to go back and downvote all of tye's nodes because they're all bad and I'd be doing a service to posterity."

Massive downvoting started afterwards and was done openly and often with explanation.

Indeed, and rather than quality of contribution improve things got worse.

Indeed, and rather than quality of contribution improve things got worse.

and voting made us feel better

Certainly this could be better worded.

Anyway I don't think this case is about sundial.

Is this an actual change to policy?

No. I'm merely codifying existing ad hoc policy. See the references I linked. There have been a few cases in the past, including one where a user was locked out for a while for voting abuse, and another had his voting privileges suspended for two years.