I was strictly making a point on something mentioned in OP, the news item that you shared lately is irrelevant to what I have said and what you were extending.
Barricades mark limit, crowd under normal circumstances maintain some distance in fact police is sandwiched between two. Besides neither they are feathers that can be wafted nor they are so light that they can be displaced easily by vibrations produced in march. Whether students or senior citizens, restricted area is restricted, no one is supposed to break through the security barriers blocking access to sensitive buildings.