Were the pork products even on the menu when he purchased his franchise?
A question I'd encourage folks to ask themselves: If he shared your religion and his objection was something that your religion proscribes, would you feel differently? If he was catholic and Dunkin Donuts wanted him to sell apple fritter communion wafers as snacks, for instance, or bottled Holy water, or you were Mormon and they introduced products with caffeine after you started, or required the restaurant to stay open on a religious holiday, how would you feel about this objection?
But in the end, I feel the real issue here is the situation that small business owners can be in when in a franchise. It reminds me of Home Owner associations, where you're paying for the privilege of losing control over your possessions. While franchise restaurants have a statistically lower failure rate, my experience has shown that it's not a silver bullet, and there are many persuasive reasons _not_ to enter into a franchise, and control over your own menu is one of them. I note that he wasn't trying to change any recipes, just that he didn't want to carry some items that he shouldn't have had to.
I suspect their enforcement is somewhat selective because, as some of the posts here show, being Muslim is in itself a reasonable reason to disregard personal concerns. The respect shown to folks of different beliefs is pretty low sometimes, and while it may be socially acceptable to classify Islamic food restrictions as "crazy" because they aren't yours, I'd hope that the small business aspect of this would overcome that.
1. He doesn't want to sell these products.
2. Other Dunkin' Donuts are allowed to not sell them.
Seems fine, and I'm suspicious about the motivations of the company that selectively enforces this rule. How will you feel when it's another company that acts arbitrarily against your religion?