Been away for a while so didn't realise this had taken off again.
To answer a couple of points:
The Union is a private members' club. Members have a right at any time to question the suitability for office of its officials, in the same way that (for example) the leadership of a political party is accountable to its members. If the leader of a political party were being investigated for similar offences, I think it would be reasonable for the membership to ask them to stand aside until the situation became clearer.
It was an open letter for members, not a petition (the clue is in the title of the thread). It was not open for anyone who was not a member or not part of the OU community to sign. I put it up here because I know that there are a lot of alumni on MN (most alumni are also Union members).
I think Sullivan has missed an opportunity to show that he can do the decent thing. If he had stood aside and subsequently heard that no charges would be brought, he could have got on with his life having shown that he can behave without self-interest for the sake of not damaging the institution he represents. Instead all he has showed is that his main priority is clinging onto his position no matter what.
Being President of the Union shouldn't just be some shiny toy or prize for the undergrad who hacks the most. It does come with some responsibility, which includes knowing when to step away if you're doing harm to the reputation of the institution.