There are many classes of topic. Many posts are considered 'on topic' for HN, some are considered 'off topic' and flagged away, and then there is a lot of grey territory which seems to be tolerated but can't exactly be labeled as 'hacker news'. Politics is the most obvious example. Should downvoting work the same way in political threads as in technology threads? It really isn't serving the same function.

Perhaps political or otherwise 'semi-topic' submissions can be flagged as such and thereby disable voting within them. People can visit them if they want to, but they do so knowing there is a different ettiquette.