To take an example from my own experience, if I automatically tuned out anyone who said something bad about the requirement to make things accessible for blind people, I would deny myself the opportunity to learn how they think and become more effective in my advocacy or, possibly, revise my position.
Yes, I mention that in the second paragraph. That's his to decide.
If you're interested in hearing the other side in all cases, then of course blocking is counter-intuitive. Wether he wants or not, it's his choice.
However, even if you were to block everyone, you could still curate the experience of hearing from the other side in other situations: by consuming articles, by asking someone privately, by not blocking some of the replies.
I also would disagree 100% that social networks are a proper venue for this kind of exchange.
He still has 100% the right to block and saying this is akin to cancellation is bullshit.
To take an example from my own experience, if I automatically tuned out anyone who said something bad about the requirement to make things accessible for blind people, I would deny myself the opportunity to learn how they think and become more effective in my advocacy or, possibly, revise my position.