I think that was the problem, in essence. The league decreed, or at least issued guidance, that the club kits should carry the poppy, but McClean refused to wear one. I don't really have an issue with that, because the people remembered by the poppy were fighting to defend individual freedom as much as anything else, so permitting him not to wear the poppy is itself an endorsement of that freedom.
Let's not credit McClean and Mullin with more intelligence and principle than they're due though. In this case, what we're dealing with is a couple of overpaid prats whose only brains are in their feet. If there is a blow to be struck for republicanism or revolution, you wouldn't pick those two idiots to advance the cause!