Why not? It's perfectly reasonable to say in a perfect world, X would be illegal if you think that X is harmful enough for the state to act. I bet there are things you wish the state would ban. You don't have to agree with the OP, but he's not expressing anything wacky or bizarre. He just doesn't see unionization as some kind of unquestionable moral good.
The reaction this guy is getting really highlights how tech has become intellectually intolerant. It seems that everyone is treating what he said as some kind of blasphemy and is personally offended that he's opposed to unionization and wants to use the state to ban the practice, as if you're not allowed to think those thoughts and remain a person in good standing. You, in fact, are allowed to think those thoughts.
It's just that we're not obliged to listen, and we're also free to express our opinion with the downvote button.