When down voting an answer, I see that I do not need to give a reason if I don't want to (Though I always make sure to let them know what is wrong). Why don't we make a rule where users have to give feedback when down voting a post?
This question comes up a lot. Like, a lot. On main meta, on other SE sites all around the network, and—yes—even right here on Puzzling Meta. I mean, really a lot.
And it's always rejected, and for good reasons.
The semi-canonical reason why there is not such a rule can be found in the expansive answer to
Why isn't providing feedback mandatory on downvotes, and why are ideas suggesting such shot down? on StackOverflow Meta; it's slightly StackOverflow-specific, but most of it applies to all SE sites. In short, downvotes are expressly anonymous and intentionally made to not require much effort to do; in particular, a downvote should not involve jumping through any more hoops to cast than an upvote, as there shouldn't be a higher psychological cost to giving a post a deserved downvote than there would be for giving an upvote.
Feel free to peruse the many prior questions and answers for voluminous other words on the subject.