If a post I'm reading is on a topic I'm not really into or dislike I simply don't vote on it at all and let it be.

On the other hand I downvote if a post is plagiarized, stealing someone elses creation, total spam, phishing, scam or illegal (pedophilia, real gore, etc).

Doesn't matter if a post is long or short, as long as the author puts a bit of themself into it, it's legit.