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If this is indeed the established cultural norm, most users would just post spam and self-upvote it.

If that's what we want, we should establish that as a community, so that those of us following the social norms are no longer game-theoretically disadvantaged.

I expect that you neglect to consider that the rewards pool is a common resource. When you upvote yourself, you draw down the rewards pool that all others depend on for their own rewards. Therefore they have a vested interest in your actions, because your actions impact their own rewards.

The rewards you just upvoted yourself will decrease the reward I may get from someone who upvotes my comment, for example.

This is why I stand on principle, and never upvote myself.

My intention is to benefit others with what I contribute. I am not very concerned with my own financial rewards (but I am weird) as I have simple needs, and meet them through work.

I hope you are able to understand that everyone that is impacted by your voting actions, and thus has not only a right, but an obligation, to judge it, and flag it if they feel it's abusive and they need to do something about it.

As you can see from the flag I DIDN'T cast, I do not feel it my obligation to be your judge. Also, my measly $.02 vote means you are safe from me. Just don't be a big meany and flag ME =p