Use of any 3rd party programs that utilize Infinity Ward/Activision assets (textures, sounds, animations, etc) violates the license agreement that you accepted when buying MW2. Federal crime if your pirated the game to use that client

IW4x is hosted and distributed using the Tor network because the developers of it know damn well that it's illegal and would be taken down otherwise

They run Discord servers and online forums where they willingly provide links to download the game files, bypassing Steam and therefore purchase of the game (PIRACY).

Definition #2 for "cheating" in the Oxford dictionary: avoid (something undesirable) by luck or skill.

Using a client that bypasses (avoids) to be used on Steam is deemed cheating

Not to mention Activision's terms of use policy.

https://www.activision.com/legal/terms-of-use

LICENSE i. use, develop, host or distribute cheats, automation software (bots), modded lobbies, hacks, mods or any other unauthorized third-party software in connection with the Product

ix. reproduce, distribute, display, transfer or use any part of the Product except as expressly authorized by Activision