The problem with this proposal is that by eliminating self-upvoting people would be able to get around it by simply setting up two dummy accounts that upvote each other. Or if you're particularly unscrupulous and wanted to get elaborate with it, you could create a dozen or so to make it look more organic. It would be very difficult to spot these unless you were dedicated to looking for it.

And while I agree that this reward pool dilution from such activity certainly is a problem for the viability of the platform, I don't think it qualifies as theft. If you hand a bunch of hungry people in a room a huge bag of tacos and then tell them all to only eat the ones that others give them for adding value, how many do you think are going to do what you ask? And what about the people who suck at life? They're still hungry. I can't begrudge a hungry someone for eating food you just waved in front of their face. The system was set up to reward this kind of behavior, so if there's a solution it needs to be built into the system, like your HF20 suggestion blocking self-upvoting (or at least limiting it in some way).

I can foresee prohibition using some sort of policing agency (even one set up by groups of users) as an opportunity for people to engage in the equivalent of "organized crime" with flag wars erupting between different interested parties. When money is on the line certain types of people can get very dedicated to this type of activity and they'll have much more energy for it than we do to stop them. We all know how this kind of thing plays out in the real world. Why would it be any different here?