The biggest problem is the lack of defense that players have against people like that.
They need to have open and closed servers like battle net did with Diablo II
The open servers allow you and ANYONE ELSE to use either a legit character OR if you wanted to, you could hack the living sh*t out of your character/save file and make your own modded weapons and crazy stats etc.
The closed servers (which is basically what R* servers are now....sort of) stored your character online on their servers and you had no access to do any kind of save file modding, so you and everyone else were all legit players.
The "hackers" had no reason to try and mess with closed servers since they had their own to run rampant on.
If R* did something like this it might work out slightly better, but they don't seem to be as good at dealing with hacks/mods like this, and there would still be the assholes who just want to rain on everybody's parade and find some way to mess with the closed servers.