Here's the thing. You would have to think on Vegas terms. Card Counting is not illegal, however if they even suspect you of doing this casinos will kick you out add you to the Griffin book (cheater list website) and you wouldn't be allowed to play in Vegas, all of Vegas ever again. That in-fact mean if you do go back then you are breaking the law.
They increase your advantage, plain and simple. However, modding a game is something we all have done. DoD is a mod, CS is a mod and originally Valve was trying to prosecute people for doing this. Being is court and such. (or discussing it i don't know for sure if it ever happened)
However, this modification is not available to all players it's a client side thing so even though I look bright pink to you you look like a regular ol' German to me. Or with the gun mod it gives you a little bit bigger Field of View, or a brighter dot. or whatever. Still and advantage
Call it what you will, even the mods that just "look" cooler would possibly give you an advantage, even if its just a mental one.
The only problem with running a "pure" server is there are mods that we all use that make the game more fun, like "medic" or even the Stats mod. While medic has an advantage, the stats don't, except maybe the mental one I was referring to earlier.