The real point here is not whether we are being brain-washed to accept wrong behaviour.
The point is that people are refusing to believe the police when they say this man constitues no danger. By which, I presume they mean that he has no criminal record and that nothing he said when interviewed made them feel he was "loitering with intent to commit a felony".
Presumably, they pointed out to him that hanging around the gates of a school, especially dressed in an approximation of a school uniform is a stupid thing to do, and will lead people to assume he is a pervert.
I really do not know what you expect the police can do in this case, or the school for that matter. Anyone may stand on a public pavement, dressed as they please, as long as their dress is not an offence against public decency.
Another point is that if people are circulating photos of this person and stating or hinting that he is a danger to children, or anyone else for that matter, they themselves are probably breaking one or two laws.
I am uncertain what English law states about circulating information and photos on the Internet . Here in Denmark you would assuredly be fined for defamation of character is you warned people against a person you could not prove was guilty of a crime.