I've read all of your posts here, and think it's worth pointing out that you sir/madam, do not understand human nature nor do you understand the real world. What you are suggesting is akin to the death penalty in the USA for example. The argument goes, that killing the worst criminals will make others think twice before following in their footsteps. Has this worked? Absolutely not. People still murder, rape, go on killing sprees and become serial killers. The punishment for the crimes, no matter how severe it is, will not act as a deterrent. To highlight my point further: Taking stationery from work, that does not belong to you, is theft, a punishable offence (job loss or even prison time), yet it's done on such a grand scale every day, why? The same as with the aforementioned other more serious crimes; the odds of being caught are why people keep doing it. If you had a 99% chance of being caught breaking any rule, even if the punishment was to have someone pee in your cornflakes (which you'd only find out after putting a spoonful in your mouth), you'd be less inclined to do it. There will always be exceptions to this rule of course, but the point still stands: Punishments themselves are oft times not much of a deterrent.
Now for your original point, about how gil buyers are the scum of the earth and how buying gil ruins the game... prey tell, how exactly it ruins the game? I'm yet to see any evidence of how the game is negatively affected by someone's decision to buy gil. Item prices are reflective of how much gil is in the economy, and what the supply for those items is. It's an accepted fact that shards are mostly supplied by bots, remove the bot owner's ability to sell gil, and they'll stop supplying materials, which puts demand up and supply down, creating hyper-inflation. As you can see, your suggestion will actually have negative consequences, and don't even get me started on how much resources you expect SE to waste investigating who got what gil from where and what items to give back to what players. I for one, would have no use for 2-3 dozen 4star items that I've made for people that used RMT gil to buy from me, and I sure as hell can not sell them all on the MB with the 30 other crafters receiving a dozen+ items.
If you really want to solve the RMT problem, ask SE to sell the gil themselves, this way they can undercut the gil sellers, pushing them out of business, all the while creating an additional income that could be put back into development of more game content, or ask them to come up with better ways of adding content that's crafted but wont fuel the market to the point people feel the need to buy gil in the first place.