This of course, is begging the question either way.
The purpose of the police is NOT to oppress. The purpose of the police is to provide an essential civil service, namely law enforcement. Law enforcement these days has a bad reputation, but without it, things would be much much worse. It is wrong to say that police have no place at a pride parade; the police provide a vital and needed service should some moron decide that "burning faggots" is a great idea, and hurls a molotov cocktail, or some other absurd hate filled action. The police not being present would only make things very very terrible. The police NEED to be there, to provide protection, FOR the people having the parade.
If the police are NOT fullfilling that civic duty, to serve and protect, then they need to be brought back into line. (Oh gawd do our current police forces need to be brought back into line...)
This is more like saying "Men aren't welcome at a women's rape counseling camp." It begs the question that all men are rapists, just like the prior begs the question that all cops are homophobic haters, and doubles down to state that there is simply no place for them there, ever. (in both examples.)
Edit-- I think it necessary as well to point out that simply because you do not want somebody or some group of people to be present at a function, does not mean you are entitled to satisfaction on that desire-- which is exactly what the "No police at the pride!" thing is.
Take for instance, white nationalism. What do you think lynch mobs, racist brutality, coopted courts, and all that BULLSHIT actually *IS*, aside from trying to make an "undesired" group not be around anymore?
Or we could go with the Middle East, and its fervent desire to drive all the Jews out, and to destroy Israel. It does not matter that Israel has been a bunch of dickheads over there-- they have a right to exist, and should not be driven out just because others who are either more powerful, or more numerous want them gone.
The irony is that the reason for the pride parades IN THE FIRST PLACE, is to demonstrate that a group that had previously been the VICTIMS of such an organized effort to expel, or eradicate the presence of, can now assemble openly, freely, and without reprisal. THEN THEY HAVE TO GO AND DO THIS SHIT.
Sorry, but NO alway. Just NO.