I disagree fairly firmly on all points
1. It's an open letter. Often the intended audience to such a letter isn't the addressee.
2. Are you able to point me towards an institution/group of people better placed to claim to speak for the majority of Rovers fans than a coalition of the club's biggest supporter groups?
3. I think this is fairly widely accepted as a way to starve out negligent owners, and outside of football, a boycott is probably the most widely recognised form of protest against a business.
4. Wholly disagree. I think it's well written, impassioned and earnest. There's no need for militant language, and I would argue that using such language would be detrimental to the cause. There are far too many people looking for a reason to discredit the coalition and their aims.