I am curious about what another way to describe the negative action of "downvoting" could be. Is there another word out there that could be used as a replacement?
In the context of electronic media there is "dislike" of course.
The first word that comes to mind is the verb fault, which is to find reason to criticize someone or something.
Obvious related verbs and phrases then come easily, including challenge, criticize, dispute, gainsay, disagree, question, call into question, discredit, disparage, belittle, denigrate, and the list goes on...
Some less formal or slang verbs and phrases include diss / dis (meaning to disrespect), flame, and trash talk.
If you want to express your disagreement on a proposal:
- To disagree
- To dissent
- To oppose
- To object
If you want to express the standard or quality of something
that justifies a downvote:
- low quality
The word nay as a noun is a vote against.
Consider the slang term, dis (or diss)
(slang, mainly US) to treat (someone) with contempt
'veto' is a good word for voting against something, even if this vote doesn't settle the issue like a political veto does.