If "they" try to stop him from voicing his opinions, you'd have a point. But "they" only stopped this person from imposing his opinions on people who had chosen instances whose policies involved a certain style of moderation.
The benefit of the fediverse is exactly that any moderation or blocks do not stop your speech - no matter if it's actually abhorrent or just unpopular with the wrong people - it merely lets people opt out of listening to you.
"style of moderation"? what does that mean? I don't agree with what GP said, but on what basis could you moderate his posts? Because they aren't "true"? In that case why not say that your instances bans all "untrue" things? how simple!
Consider HN. Try to post a thread of puns here, and you will be flagged. Do it often enough, and you will be blocked. That is a style of moderation.
Consider Reddit. Post pun threads there and you'll likely be heavily upvoted instead. That is a different style of moderation.
To take more extreme examples, there are fediverse instances that consider racism to be ok, and there are instances who don't consider it ok but won't block other instances as a matter of principle, and there are instances who will block whole instances if they don't moderate racism. Those are all styles of moderation.
You have a choice in which rules are right for you. You might want a highly curated environment (like HN), or a more freewheeling one (like Reddit), or a near total free-for-all (like 4chan). Which one you pick may determine who else are willing to talk to you, because some dislike eachother - whether justified or not - enough to not want to talk to each other. If I want an instance that blocks people who like dogs on sight, I'm free to do so, and you're free to consider it an idiotic policy and not join my instance.
Nothing stops you from having more than one account if you want a mix of environments who don't get along.
Christ. This isn't the government censoring opinions. This is people kicking others out of their bar for not following the social rules and norms in that bar. They can go to another bar. The basis is: "we don't want that behaviour here" and that is ok when there are alternatives.
The benefit of the fediverse is exactly that any moderation or blocks do not stop your speech - no matter if it's actually abhorrent or just unpopular with the wrong people - it merely lets people opt out of listening to you.