That's not a very good comparison, as the victim there has no wishes to take into account.
Let's invent a fictitious party called something like the Revolutionary Workers Party. Let's say that within such a party, one member in a senior position, Mr Z, is accused of carrying out a serious sexual assault on another member, Ms E. Ms E does not want to go to the cops because she is traumatised by the whole experience, has a very sceptical view of how the justice system treats sexual assault complainants, etc. However, she does want Mr Z gone from her political organisation and from any position of authority over her or others.
Now, lets say that the RWP actually advises Ms E. to go to the cops, but she is still opposed to so doing. Going to the cops without her consent (a) is a rather brutal thing to do to her and (b) - this is absolutely crucial - will still not allow the RWP to evade doing something itself. Think about it for a moment. Let's assume the RWP suspend Mr Z without prejudice and then leave the state machinery to do its job. What then?
The state machinery has many of its own flaws, to put it mildly, in how it deals with this kind of allegation. And even if it where to operate as it is "supposed" to do, it is looking into a different question. It is there, effectively, to determine whether it can be proven beyond a reasonable doubt that Mr Z is guilty of the serious allegations and should be locked up. But the RWP's question should be different - has Mr Z probably behaved in a way incompatible with party membership. There are many circumstances where the answer to the state's question may be "no", including circumstances where the state did something wrong and circumstances where it did everything by its own book, while the answer to the party's question would be yes. Even where the state investigates, the organisation still needs a way to determine the answer to its own question. The same applies to unions etc.