Isn’t it that people should vote down everything they disagree with?
Not really. The usual convention is “vote down what you want to see less of.” People differ in terms of what they want to see less of. For example, some people downvote poorly-reasoned arguments defending positions they agree with, because they want fewer poorly-reasoned arguments. Some people downvote well-reasoned arguments defending positions they agree with about topic X, because they want fewer discussions of topic X. Some people downvote well-reasoned arguments defending positions they agree with in response to known or suspected trolls, because they want fewer response to trolls. Etc.
Not really. The usual convention is “vote down what you want to see less of.” People differ in terms of what they want to see less of. For example, some people downvote poorly-reasoned arguments defending positions they agree with, because they want fewer poorly-reasoned arguments. Some people downvote well-reasoned arguments defending positions they agree with about topic X, because they want fewer discussions of topic X. Some people downvote well-reasoned arguments defending positions they agree with in response to known or suspected trolls, because they want fewer response to trolls. Etc.