I think one of the bit arguments against is that by design SE is supposed to be aggressively meritocratic. By blocking yourself from seeing specific users - you're more or less making it about the poster not the content.
As per the original question and many of the answers - well we shouldn't be seeing flamebait if people focus on the problems at hand. Even on the newer, subjective sites, I think our core goal - to get people useful, practical answers to real problems is important.
However with broadening scopes, not all sites have objective, purely technical scopes so having this as a option on some sites could be worth considering, other than these sites have more problems with folks not getting along, not less and being able to hide posts kind of just sticks a bandaid over a broader issue.
I can see some people benefiting from being able to block seeing comments but blocks on posts feels kind of against the 'ethos' of SE as a whole.