Let me reiterate this again, for clarity:
I'm saying that monolithic organizations like law enforcement aren't comparable to a loose coalition of protesters, because there's vastly more authority behind law enforcement than said loose coalition; if a police officer detains someone, violently or otherwise, then they do so with the full weight of that institution behind them. They're also far less susceptible to infiltration and internal sabotage, incitement to sedition (valid or otherwise), and the like. When the people feel that injustices are being committed upon them by those in authority, protest -- peaceful or otherwise -- is their only recourse. The law is not an option when the law is an issue.
Both side should be held accountable, but there's also the matter of how that accountability is treated in terms of the weight behind those in a position of authority, in addition to other extenuating factors.
A small contingent of "protesters" does not fairly nor accurately represent the larger movement due to less internal cohesion, and are often rightly condemned by those inside the movement when they step out of line; those in authority, however, do represent the uniform they wear at all times. When there is undeniable evidence of repeated police brutality, it generates a call to hold those who committed these horrific acts responsible, in order to preserve the virtue represented by that badge -- otherwise, what it represents eventually becomes not only meaningless, but a symbol of tyranny.