still a simple checkbox with a few well chosen reasons would be valuable. At the very least it would make you actually think of why you choose to downvote that specific comment. There are many nuances of disagreement, some deserving a downvote some not.

It's not going to be valuable. Would a simple checkbox with a few well-chosen reasons be valuable for upvotes? The difference isn't nuance or opportunity for self-improvement, it's just that getting downvoted feels bad and getting upvoted doesn't.

Whether it's "logical" in a universal sense is debatable, but removing a common known frustration of users is usually a good thing regardless. If purple walls anger your customers, then repaint them rather than argue that purple is logically better.

I didn't say it was 'logical' nor did I say dealing reducing user frustration is bad. Trying to address user frustration in this specific way is ill-considered and bad.