The main reason for an FPS limit is to counter stupidity. You're always going to get a noob who doesn't know better, or someone will panic and open up on somebody at a range where they have no business pulling the trigger. My brother has taken a 450 FPS shot to the face from 20 feet from a sniper and that was just a mistake instead of stupidity. 350 FPS is more than adequate for a CQB field. Firing down a hall, your BB would reach it's target in under 0.2 seconds. Putting this into perspective...
Distance : 70 feet
Speed : 350 fps
Time to target : 0.2 seconds
Time to hear the shot : 0.06 seconds
Time to react : 0.14 seconds
Average human reaction time : 0.195 seconds
Only someone with a superhuman reaction time would be able to avoid being hit, assuming your shot was actually accurate. That's time to REACT, and doesn't take into account the time it would take to physically move.
When it comes to using .177 pellet guns to play, that's incredibly stupid. Unless you're using a pellet gun which shoots under 200 FPS, it is technically possible to hit and kill someone with one of those. If there's people dumb enough to shoot each other with pellet guns, then there's people dumb enough to use pest control ammunition. I have a CO2 powered little P99 which will put a round through a T-bone and 2" of cork board at 30 feet using pest control. If I hit someone between the ribs, I could puncture a lung or worse. Even wearing full face protection, you could hit someone in the neck, back of the head, etc.
"You want to talk to God ? Let's go see him together, I haven't got anything better to do."