I'll tell you exactly why I don't like client anti-cheat. Before I got involved with GTA multiplayer mods, I was a big America's Army player. I had ~50 honor. America's Army used 'Punkbuster' for anti-cheat. I have never cheated in any online game. When you use hacks, you're not only ruining the game for other players, you're ruining it for yourself. Punkbuster had a player screenshot mechanism that server admins could use to check for players running hack overlays. After I upgraded my video card, Punkbuster for some reason couldn't get a screenshot and the admins on the server I played on started accusing me of running hacks. I was fairly pissed with the accusation and didn't like the idea of client-side AC since.

SA-MP did have a client AC at one point called SAC, which wasn't developed by me. I allowed SAC to run for 6 months or so and SA-MP's total player count stalled around 4000. A lot of players were having trouble automatically downloading new SAC versions. The problem was similar to Punkbuster updates. One of the developers on the team who got kicked out, decided to leak the SA-MP source code on piratebay; around the 0.2.5 timeframe, which included SAC's private signing encryption keys. That was the nail in the coffin for SAC. A few months after removing SAC, SA-MP's player count went from 4000 to 8000, proving that a lot of people had problems with it.

What I've tried to do in place of client-side AC is give server owners enough tools in the server script to at least prevent hackers from being able to ruin the game for other players.

I think a lot of SA-MP players appreciate the fact that SA-MP isn't invasive and the server owners aren't able to constantly probe your computer or GTA:SA installation. Some client-side AC is borderline spyware. (C) Kalcor