This would cause more money in the economy, not take more out. People who want their heads usually pay someone money plus the 5K used to set the bounty.

 

User-User money exchange doesn't affect the amount of money in the economy. Also, out of the minimum 5k used to set a bounty, only 10% ($500) is truly taken out of the economy, as the rest is then given to whoever accepted it and killed the designated player.