[OkayPhysicist]

Large organizations are in a middle ground between "You are forced to participate" nation-state groups and "Leave at any time with little impact" groups like a small club or friend group. Different levels of proof are appropriate at these various levels. For a nation-state, you need to be damn sure before levying a punishment, because the impact of punishment is much greater. The trade off is a much more rigorous investigation of potential wrong-doing, and a certain level of acceptable false negatives. It's better for a nation-state to let a couple people get away with crimes versus falsely convicting someone. In a small, informal group, the greatest punishment they can issue is a relatively low-impact exile, so levels of proof can be extremely low: a vaguely plausible rumor will probably get someone kicked out.

Big organizations like universities, chess leagues, and workplaces are in a middle ground. Exile from such a group is a much bigger deal, as it can threaten someone's livelihood, future, or incur other fairly large opportunity costs. However, they can't throw someone in prison, so compared to the nation state they need less confidence to levy their punishments, and thus are expected to be less accepting of members getting away with inappropriate behavior.

All of this comes to head with the issue of sexual harassment and assault. It's a very hard category of crime to prove "beyond a reasonable doubt", because often the only witnesses are the victim/accuser and the perpetrator/accused. If an organization takes a stance of only kicking someone out when they are convicted in a court of law, they are stating that they are willing to accept some level of misconduct, which is greater than most would like.