I've always been surprised that Danton would slag someone off for having a vice! Or is it some off-the-cuff comment he made that becomes a 'shameful vice' when filtered through Robespierre-consciousness? So it could be anything....!
It could, if he means deviances as applied to writing, be laudanum (look at his English contemporary, Coleridge, total junkie!) - Desmoulins was having health problems at the time...