I don't think there is any current rule or dominant etiquette around down-voting, only people that follow different rules or etiquettes, all of them self-impose

I don't think there is any current rule or dominant etiquette around down-voting, only people that follow different rules or etiquettes, all of them self-imposed. Since Paul Graham is fine with down-voting for disagreement (http://news.ycombinator.com/item?id=117171 http://news.ycombinator.com/item?id=117171), you can't really object if others do the same. I recommend just taking karma points less seriously.