I personally made a rule of upvoting any content with net negative score which doesn't deserve a downvote, even if I disagree

I donwvoted you, because you seem to use upvotes in a way that diminishes the value of the karma system in my eyes - an undeserved downvote is as bad as an undeserved upvote.

I've seen a lot of low quality posts getting some karma, and coming back to positive scores without a good reason - and now I know the behaviour that is partially responsible.

(and the above comes from someone with a mass downvoter after him, who gets a downvote on every single comment he makes)