same amount (or even more) of negativity comes from wilderness just as it comes from duel arena. you just notice it less, because half of the players in wilderness are quite competent, while the other half are just the same as in duel arena. in case of duel arena, 80% of the players are "flamers" who don't know how to accept defeat and only want to make quick money, while other, 20% act politely and accept defeat.
imo the the solution to that would be to actually reward players for being nice and condemn the players that flame to much more severe punishments. considering that most of the players, that are that way, don't usually visit forums, that should be constantly published while opening the client and (optional) in game. if that's not the case you'd want to go with, do competitions like "the most helpful, or competent players in emps scape" on forums and reward them.
removing the gambling from the game won't work...EVER, because if it is removed, instead of staker's negativity being concentrated to each other and the community, it'll be centered towards the staff and the development team.