Unless I'm misunderstanding your post and the point you're making, you're suggesting that you need a multi-core CPU in order to run the extra threads, I.e. That you cannot have multiple threads co-existing on the same core. This is not true, you could run all of the threads on a single physical core if you wished.
But even joining through Steam, the problem I was trying to point out is that by the time the first person has joined, some of the slots required for your group may have been taken. In other words, the group joining is not an "atomic operation", I.e. Taking place at the same time.
Secondly, when Steam tried to split modified servers up properly with the second list, they were met by an angry mob and server owners who would try and fool the system to get their modded server on the normal list. It's actually quite hard to not find a non-modded server with free slots and the map you want.
Using MW2 as an example, some of the undesirable modifications which have been done are low gravity, infinite ammo and XP changes - All of which mess up the balance of XP and in some case allow easy stats boosting.
I've actually seen very few players on MW2 who are defiantly cheating, yet I've heard plenty of people shooting at others who are clearly not. How would you feel if you were to be very good at the game, get accused of cheating and getting votekicked or banned by some sore player ? I'm not saying that it wouldn't help some situations, but I think it would disrupt the game for some of the better players out there. Let's not forget the countless players who would get kicked or banned for "noob tubing" and "camping".

