Innocent until proven guilty is a silencing tactic in which it is argued that any harmful action that did not result in a criminal conviction must not result in any repercussions to the person who did the action, often to the point where it is insisted that they are entitled to have everyone believe that the action did not take place at all, let alone censure them in any way for it.

It is based on the same principle that is held central in many legal systems.

Problems with this stance include:

not all harmful actions actually being illegal in the first place (for example, many jurisdictions only make sexual harassment an offense in the workplace, if then)
the considerable time, energy and monetary burden assumed by victims who report harmful acts, in interacting with the police, lawyers and the judicial system
evidence of considerable underreporting of harm to oppressed groups, lack of prosecution when reported, and low rates of conviction when tried
the nation-state is a very powerful entity, typically having effectively unlimited financial resources and reserving the right to commit violence to itself, against which almost any individual person has a considerable disadvantage. It makes sense to hold such an entity to extremely strict burden of proof in exercising its power, relative to, say, a geek conference or meetup!
the fact that in fact it may even benefit the perpetrator to face social and/or professional censure, relative to punishment by the state
In practice, insisting that the geek community only censure those who have been found guilty of harm in a court of law limits censure to a very very small number of people relative to the number of harassers and abusers within it (and within society in general).

Related stances include, eg, the position that accusations of harassment events should be tried in an open public hearing of community members or before an informal jury, etc.