Im not exactly sure how to explain this, so Im just gona go with it and hope it makes sense.
Basically, airsofters play on paintball fields because, they are a safe place to gather and play, where the field owners have agreed to allow us to play. With in the safety and confines of there personal owned land that is liscened and insuranced for said style of game play (specfically for paintball but I suppose we can sneak airsoft into there somewhere, Im winging it here common)
If a bunch of genius yahoos show up on random forest land and start hosing each other down, a passer by who sees this could wonder whats going on, why do those people have Guns? why are they shooting at each other? Next thing you know the police/rcmp get called they come take your guns away, and in the worst imagineble situation someone gets shot because an officer/constable thought that someone brandishing an a TM m4 was a immediate threat that required to be neautralised.