There's a lot of factors. How much will it cost? How much publicity will it generate and is that worse than just letting it go? What is the standard of proof that must be met and are they confident they can prove that it's a false statement? What are the consequences if they somehow fail to meet that burden? Etc.
Also, how did the left become the party of "if he's in the courtroom he must be guilty of something"?
If someone wants to clear their name, go to court and sue for slander. If it's two people's word against each other, I'll believe the victim every time since there's such a high cost of coming forward and slander laws exist.
EDIT Since I'm now throttled...
I'm saying that coming forward either means:
1. Something really happened to you.
2. You're breaking the law and can be punished.
High stakes, no? Which is one of the many reasons false accusations are exceedingly rare if not non-existent.
I will always believe the victim unless the perpetrator wins a libel case. It's the legal mechanism for fighting back.
Not the person to whom you're replying, but the presumption of innocence means this exactly. If you are accused of a crime, you are presumed innocent until it can be proven you're not.
The sword cuts both ways.
Except it doesn't, because if you're in the news for {serious crime} and later clear your name, your reputation is still probably trashed. There is no real mechanism for recovery in the modern panopticon. Lowering standards of evidence required for conviction (to basically nothing, if some people are taken seriously) is such a kludgy, cumbersome hack to solve this problem that it shocks me that people present it seriously. It's utopian thinking.