You may very well be right. Due to free-riding and buck-passing I’d still expect a lot of them to do nothing.
Recall also that they’re all in internal power struggles over ink monopolies and what have you, plus Lucius lack of complete control has already been pointed out by Lucius.
For all those who think the blood debt will hurt their rivals more than themselves there’s good reason not to change the framing of the debt. Not to forget being the one to start this campaign will be both financially and politically costly. A beautiful collective action problem. Either way, we’ve too little insights into the political power balances to make qualified estimates about the “wall-paper’s” reaction.
Why do you not consider Snape to be an alternative? Yes, Quirrelmort has gained a lot by Hat’s actions, but: a) Quirrel could be manipulating Snape. b) Quirrelmort probably has an extremely accurate mental model of Snape.
What is your mental model of Snape?