Too many misconceptions here. Police Officers are not soldiers, and airsoft is not paintball, so all that crap can be pushed aside as is. The issue is POLICE playing AIRSOFT, thats it.
Its considered Conduct Unbecoming of an Officer. its on the same level as an officer getting piss drunk in public and can result in job-loss just as fast. Its perfectly LEGAL for them to play, but thats not the same as being Allowed to play. Just like its LEGAL to get a tongue piercing, but not all jobs allow that on their employees.
after speaking with a few members of the force who had to leave airsoft because of this, it appeared that the likelyhood of losing your job from the sport is quite small, but if they ever wanted a reason to fire you, (say you piss off the wrong person), well, you can figure out the rest im sure.