It's not a matter of guilt, it's a matter of profitability. If there were advertisers beating down their doors now to get their products placed alongside Russel Brand's face they'd leave him monetised. YouTube is truly neutral here, they are just revenue maximizing, don't mistake this for a moral position. If they make a statement later, it'll be for ROI as well.

But that doesn't quite line up with what is going on. They did not remove his videos, they demonetized them. Youtube is still running ads on Brand's videos, so the content is still being paid for by advertisers. If advertisers were beating down their doors then there would be no advertising on those videos.

Can't advertisers just explicitly ask not to have their ads run on RB's contents? Why would YT have to take this decision for them?

Well it's an aggregate. Advertisers don't want to spend money on a platform that allowed Russel Brand to make money. The problem with advertiser's and the public is that platforms are seen as whole. Advertising on the platform is seen as a vague approval of the platform as a whole.

There are plenty of rappers monetizing their videos. King Von was never demonetized despite being known to have killed at least 7 people. That is much worse than what Brand is alleged to have done. So this isn't a moral judgement, this is a business decision.

But isn't the profitability issue linked to his already being "found" to be guilty?

Innocent until proven guilty is a standard for court proceedings. I am not a court, and I can even disagree with what a court decides. I can use my own judgment to draw conclusions and form opinions. For example, I can be confident that OJ is a murderer even though be was not convicted and was declared not guilty.

This is a category error. Courts use a methodology that's the best one we have for discovering the truth. They don't always do it well (e.g. the OJ case) and you as an individual can use the same methodology to understand if something happened or not. It's the methodology, not the "being a court" that is key.

I as an individual do not have the powers of a court, and cannot do the things a court can do to ACTUALLY get close to "the truth", and must rely on what little information I am allowed to have.

Absolutely. And if that information means you don't know, then you don't know.

YouTube does not have the power to assign guilt. They are exercising a contractual privilege agreed to by Mr. Brand when he decided to upload videos to their platform.