In my opinion, you're doing a great job by not enabling downvotes. Every user can see how many votes their comment has, which should be enough for them to gauge how well their comment is received. 👍

I haven’t been on Stack Overflow for a long time (around 15 years ago). Back then, I was mostly focused on statistics and programming in R. It’s true that rude responses were rare, especially in the sense that the OP should have known the answer beforehand or could have researched it themselves before asking. But yes, I never saw personal attacks.