The problem with a slogan like "believe the victims" is that the term "believe" can cover many kinds of behavior, and from different levels of authority. What you'd ask your closest friend to do is different from what you'd ask the police to do.
From an authority standpoint, I think "believe" means to presume long enough to begin investigating, that the person is coming forward in good faith. That may prove untrue during investigation -- they may be lying, mistaken, have impaired perception of the situation--but to me the presumption is not a judgement on the accused--just an assurance that an accusation will get a fair hearing.
"If fighting is sure to result in victory, then you must fight! Sun Tzu said that, and I'd say he knows a little bit more about fighting than you do, pal, because he invented it, and then he perfected it so that no living man could best him in the ring of honor. Then, he used his fight money to buy two of every animal on earth, and then he herded them onto a boat, and then he beat the crap out of every single one. And from that day forward any time a bunch of animals are together in one place it's called a zoo! (Beat) Unless it's a farm!"