Obviously, we should take women who say that they've been raped seriously. Rape is underreported, false accusations are rare, and given the skepticism and abuse that's often thrown at women who do come forward, how we react to any particular allegation affects whether women in the future feel safe reporting rape. The way we treat a rape victim in the present redounds to countless more rape victims in the future, and it's important to create a future where rape victims aren't afraid or ashamed to stand up for themselves and seek justice.
Similarly, we should take those who are accused of rape seriously when they say they didn't commit the crime. Although false accusations are rare, they're not unheard of, and if a man is the (statistically unfortunate) victim of a lie, it can destroy his life -- a cloud of suspicion can follow him, even if there's an official exoneration. Though it's not at all comparable to being a victim of rape, being a victim of a false accusation of rape is still terrible and its own sort of tragedy.
Saying "take the accusers and the accused seriously," of course, is nice and pat and somewhat unrealistic. Everybody has their own experiences and gut instincts, and jurors in the court of public opinion aren't bound by any legal standard on which to base a verdict. ("Presumed innocent until proven guilty" doesn't apply out of a courtroom, after all.)
So when some people recoil at the idea of a beloved figure like Bill Cosby being a rapist, it's not exactly surprising. (Look at a supposedly progressive MSNBC host named Joy Reid and her guest discuss the allegations -- not with concern for the alleged victims or the problem of rape, but by fretting over how Cosby's legacy is on the line and how he can manage the crisis, because, you know, journalism.) What's decidedly not okay is when the recoiling takes the form of automatic, knee-jerk dismissals.
Women who come forward with rape allegations are often put in a no-win situation, where every action or inaction is "proof" that they're lying or crazy or greedy or attention-hungry. Nobody is saying we have to automatically believe every rape accusation with complete certitude irrespective of the evidence and circumstances, but we shouldn't automatically disbelieve every one, either.