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The reason why so many people dislike self-vote is that each vote directs a bit of the steems on the reward pool toward the post that's voted on.

As a result, if you self-vote, you are deciding unilaterally that your post is of good quality enough to be a reward. It might be inconsequential if you upvote your own "real quality" post with a low-SP account. But when your vote takes 100$ out of the reward pool toward a 10-word post, now that's abuse.

Plus the quality is a very subjective matter... what you think is quality isn't what other thinks is quality, as a result, thus self-vote becomes a sensitive question, don't you think?