we should believe accusers long enough to find out whether their accusations are accurate
I always want to keep an open mind until we get more detail, and I bear in mind with rape that it's an underreported crime and statistically the vast majority of accusations that go before the courts have merit (not sure about stats around pressuring people to do sex acts or fat shaming).
The exhortation to "believe" outright always troubled me but thanks to your comment I see what it means is that people to be in a mindframe where they can believe as in finding out - it's not an exhortation to prejudice (in the literal sense of the word).