Those who shared information with the Gestapo about where Jews were hiding were knowing accomplices in genocide.
They can be responsible for that, if there is evidence to support it, without being responsible for the arrest. Holding the jewish person at the end of the long chain of actions 'responsible' for the whole situation doesn't really seem that much different from blaming the victims themselves.
But this sort of 'posthumous trial by media' is revolting in its own right, especially because the instigators are simply trying to make a buck off the back of Anne Frank (they're not the first and likely won't be the last).
Apparently the theory is that he gave up this family to save his own family, which is a horrific situation to be in. So even if we knew this is what actually happened, and we don't, it's an obvious mitigating circumstance.