At some point the private platform becomes so influential over the information environment and politics that it can no longer be considered merely a private platform. It is now also a public square. It’s not unreasonable at that point to require it to adhere higher standards of evidence, law, and reason.
In this case, I’m no fan of Brand, but I’m even less a fan of YouTube’s apparent policy of “guilty till proven innocent” here. How about waiting till he and his accuser/s have had their day in a court, and jury of peers weighs the evidence and decides his guilt?