I see no reason to remove the negative karma button. I think it is a good tool for all forum users with which they can express or in some way punish the bad behavior of other users, among other things, such as disrespect, insults, possible scams and more. As a user I only use positive karma, but as a moderator I don't need it, since I have other types of tools.
As we have said on other occasions, the abuse of negative karma to “attack” a user is unlikely if not impossible, since with the restrictions of the karma system, (only every 10 hours) no user or group of users would have time to do something before the administrator resolves the problem, so I think there is nothing to worry about.