Should the police not be involved?
No, this is sufficient punishment from the court of public opinion.
There is (rightly) a very high standard of proof required in the context of criminal trials that (rightly) doesn't apply to other contexts. And even in the context of criminal trials, the presumption of innocence isn't absolute.
The term doesn't mean someone needs to be proven guilty in a court of law before you can confidently form your own opinion of them or their actions. It also doesn't mean people aren't entitled to, say, decline to give him an industry awards, decline to work with him, decline to employ him, decline to associate with him or publicly criticise him without the allegations having been proven beyond doubt in court. In all those contexts people are allowed to draw their own very solid conclusions based on 20 different women accusing him of misconduct.
People are allowed to do whatever they want personally. Boycott his albums and what not, or whatever he makes. However when it's tantamount to blacklisting someone based on allegations that can't be proven or at least examined, then "yeah it's not an actual court so I can feel how I feel" isn't a sturdy defense. BAFTA had the original correct response, declining to act based on not being able to vet the veracity of these accusations.
And it's only when it comes to sexual accusations that the number of accusations (on different events mind, not 20 witnesses to one single crime) is sufficient for a block of the public to go, "yeah that's enough, ban him, but only ban him, don't trouble the police".
But meh, he'll go into hiding for a few months, come out on an "apology" tour, and life will go on.