Most of the time I cave. But lately I've been thinking harder. Of course I've known all along that one less person grabbing the candy and one less person eating a cupcake does—if you really follow it's effect down the line—make a difference. If there's consistently less of a demand, even by a factor of one-fiftieth (I work in an office of about 50 people), then maybe the person who orders the cupcakes will eventually buy fewer—maybe will even buy two fewer since I often eat more than one.
There is such a thing as vegan doughnuts, and the ones at BabyCakes NYC are better than anything at Krispy Kreme or Dunkin' Donuts—and healthier (they're not deep-fried). Unfortunately, I don't live in New York, only visit.
As for cupcakes, I'm pleased that in DC, both Hello Cupcake and Red Velvet Cupcakery have a vegan option.
I made my own cupcakes this week—coconut—from Vegan with a Vengeance—and liked them a lot. The cake part is probably better than that of either of the above shops. The frosting, made with coconut milk, nondairy shortening, and powdered sugar, was a little sweeter than I'd like, but I wanted to use it all up, so part of the problem was just the quantity. Next time I'll go easier and save the leftover. And will try it with low-fat coconut milk. But they're excellent.