I'm generally of the opinion that players shouldn't be able to cheat online in general. Addons are fine for the most part, things like levels, characters, music, even cheats that are tied to an addon and only work with it loaded. Cheats built into the game itself however, or even worse clientside cheats like what happened back when SMS Unleashed first came out should be avoided as much as possible online, to keep things fair for all involved.
Noclip in particular has a number of uses that a player could use to their advantage, especially in PvP gametypes. Paired up with godmode, it could be especially unfair.