There is plenty to gain from downvoting. It keeps the reward pool healthy, it democratizes and diversifies the distribution of rewards, and also there is a curation reward. Who's not to like downvotes?
There is a downside though. There are people who own a lot of stake, and if they don't like you, they can strike your posts down one by one, making you lose all your hopes of ever getting rewards from anything you post, no matter how good the quality is.
Chipping away a small fraction from the potential rewards of someone's selfie because it doesn't look like worth it is not comparable though.