Write, phone, protest outside the stadium, do whatever is correct and lawful.
But don't abuse Brewster with vituperation, expletives, wild angry language etc. That will NOT inspire him, or the players who will only get more depressed. No one deserves that .
Brew may be wrong in his tactics ,decisions, etc --or NOT. However there is no one on here who has proved he is totally at fault and it is reasonable to suppose that he has done HIS best. If so, what more can he do?
So what are your reasons for suggesting intemperate, slanging, vitriolic attacks? It might make you feel better --or make you look stupid---or even get you slung out, but I doubt that it will influence anyone in a senior position overly.
You are not the only ones frustrated and depressed--remember that.
You are beginning to sound like a lynch mob --stop it before you will regret it.
There already is lowered confidence amongst the players and probably Management. But it is up to them to decide what should be done and when and how to do it.
Otherwise you always have the option of either getting behind the TEAM --or simply walking away.