All I see is a bunch of teenagers griping.
Put yourselves in the business owner's shoes. You have a bunch of people who are blocking lawful traffic into and out of both your store and the parking lot, which in and of itself is dangerous, and you have it within your ability to break up the gathering. Either by calling the police, and generating bad feelings which might lead to vandalism, or by installing this sound device which is sub-audible, but very effective.
Bear in mind, no one is saying anyone can't gather where they please, just which bits of private property they can do it on.