It's remarkable how callouslness & cruelty, how "fuck these people why should i give them any slack" options like you present run roughshod over civility. It's beyond words to me that such absolutely dejectable, hostile, negative, piss-off-and-die fucking-you attitude as you present is allowed to ride so high & mighty, that we believe that tension & disagreement, that some occasional fuckery means all those fuckers can all just fuck off and die. This is never going to beget a rising up, a better society. It will lead only to tension. And it's built in, at the deepest technical layers: an increased amplification of tension & pissery.
It is cancel culture. And it's amplified enormously by technical systems which don't have options like digital juries, don't have options for justice to be enacted, which afford only digital death to the other. Fuck this times a million. This is callous bullshit we exist in, and the enormousness of people being bad online isn't some weak-kneed shit ass justification for being bastards to one another like you claim: it's part of the fucking problem, and it is cancel culture. 100%. Saying that the fucker deserved it, that there's so many fuckers about, doesn't make it less so.
We do need defense. But fucking a!!! Not like this.
Stross blog has a user known as "the seagull" who creates new accounts frequently and spams vulgarity daily. She knows Stross personally and apparently he has decreed that she is allowed to do that. So a lot of his readers install plugins to suppress her comments... and have to regularly block new accounts that she creates (she has a very distinctive posting style)
Even if they were, they aren't inherently infinite or remorseless; they aren't permanent and irrevocable. (And, on some platforms, they aren't even total when in place.)
And, as most algorithms require a certain level of positive engagement to retain the baseline visibility even of something you aren't actively following, most platforms have at least one more, less extreme, negative signal—don’t positively engage with the content you don't like.
So, no, blocking accounts is not only acceptable, but the only line of defense for someone who still wishes to engage in honest discourse on those platforms.
This is not technology thoughtlessly trampling over human dignity; this is human nature expressing itself within a certain environment.
This is me realizing I cannot suckle off the financial teet of my parents and the state; and I actually must go out, make money, and keep my "work life" balance in-check -- because I'm a bag of meat with a reward-behavior system that needs certain things to remain functioning.
Online discussion is where I get my "fix." It's one source of stimulation that keeps me functioning at my best, and prevents me from degrading into a certain state of being that my biology considers "not good" -- one where I cannot meet the goals my entire mind and body have decided are "to be done."
I'm not some nobleman's son living in utter luxury and leisure. I do not have the resources available to live in an "ideal" world where I can spend my time worrying about the ultimate repercussions of blocking someone. I live in the "real" world, where I have to manage the repercussions of my own actions against my goals, and take into account how seriously engaging some nitwit on an online shit-flinging message board is going to affect my goals, and therefore my feelings and behaviors.
One could make an argument here that material inequality (and its great disparity between the two ends) has lead us to such a state of affairs; and that man's greatest faults are caused by his greatest sufferings: a system that breaks him down, and grinds away at this soul, preventing him from living a life predicated on ideals, and some greater cultural values.
But to disparage the tools which man made to try and adapt to the circumstances of his environment is silly.
I could choose to become a hermit, and live a life of anarchist pacifism, in order to live an exemplified life of idealism; but I don't want to.