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I don't think it's wrong to do that. If not there won't be that place to tick, for self upvote, while submitting post. Though I once saw a dude[name withheld for security purposes :)] who upvotes ONLY himself. Not a single upvote to another steemian. But its a free country. Lol

There's nothing wrong with doing it once or twice. Just don't form a habit of doing it.