> Where you say reasonable, I think you mean to say mainstream

Able to be reasoned with?

Mainstream pertains to "ideas, attitudes or activities" [1]. A protest probably wants to appeal to those who hold mainstream views. Or bring its supporters' views into the mainstream. But the whole point of the protest is something isn't mainstream that should be.

[1] https://www.lexico.com/en/definition/mainstream

Reasonable seems valid. With the information they had, those New Yorkers reasoned that the police were doing a good job. Likewise if you were to bring them new information, they might reason that the police are doing a bad job. And there are also reasonable people who think the police are doing a bad job, they were just exposed to a different set of information and/or different values than the people who think the police are doing a good job.

And then on the extremes are the unreasonable people. Those who will support the police regardless of any negative change, and those who will oppose the police regardless of any positive change.