It could be done away with and Hive will still function and posts will be rewarded.

It would increase spam accounts making garbage content if there was no downvote.

But downvotes were a solution for a problem 5 years ago. Its 5 years later and there are much better ways of dealing with spammers, and there is blacklists, witnesses could just vote that accounts found tk be spamming or plagiarizing cant get rewards for example. Theres a lot of things that could be done differently