There are training courses for drills and tactics with M4's, those operate with government approval, and you and your buddies can go to ranges are go practice what you've learned. That could easily be construed as terrorist training, but it's 100% legal.
If you want this to be black and white, then yes it's technically against the law. But what judge is going to convict you of playing a sport? The law isn't black and white and it's not enforced by a robot. There's still a person at the other end that needs to prove beyond all reasonable doubt that you are playing airsoft for the purpose of training to do something illegal.
I've played for years, had plenty of peace officers stop by at games we were running, the police was always 100% aware of what we were doing at any given field.
I've received training from various serving and retired veterans, and from guys that have taken dozens of tactical courses. Obviously I practice and employ everything I've learned.
But it's all for the sake of being proficient at my sport.
Stop trying to make a 20 year old sport illegal just because you misinterpreted a law. You're being paranoid.
What is with these sky-is-falling, airsoft is illegal, threads this year?