But for a scary movie, the person has elected to it.
In harassment, the target person(s) have not consented to the distress and the party perpetrating the harassment does it with the intent of causing said unwanted distress for a certain end. So yes, scary movies could be considered harassment, but as the viewing party expects to be scared, it is not illegal.
I may go there and assemble, but I will leave in five minutes because my head hurts so much. It prevents people below the age of 25 from assembling through use of physical pain, not through use of legal action. The articles granting the right to assemble do not specify that prohibition of assembly can only be accomplished by arrest and that all other methods are fair game. They say, flat out, that inhibition of assemble in general is illegal. Since no one method is specified, we must conclude all methods are prohibited. This means that anything intended to prevent people gathering, no matter what it is, as long as the gathering is lawful, is illegal.
True, a business making a sound does not constitute harassment if it is a side effect of the business's normal operation. The moment you begin to intentionally disturb any party without their consent, the moment you go beyond what is normal/acceptable with an intent to cause upset or disturbance, you have entered the realm of harassment. If you were to turn on your stereo at max when someone has requested it be turned down, that is harassment. If you crank over your AC when someone has requested it be turned off, that is harassment. If a business starts making a sound that is intended to drive people off, that is harassment through its aggressive nature.