As I've said hundreds of times before, how many other games do you know that allow cheating? None, so why should MTA be any different?
I think you're blurring the line between cheating and modding. Cheating benefits no-one. If you have a cheat server, it just becomes a contest to see who can download the best cheats. Modding can be good, but the team want a stable release before they allow it (otherwise it becomes confusing because they won't know if a bug report is a fault with MTA or a fault with a mod that someone's downloaded).