I'm sure TL gets dozens of requests daily from players who have made "innocent mistakes" that "needed to be corrected." Their repeated response has been that we have to live with our mistakes. So I can't cut them slack on this one.
I personally believe TL should have given everyone a couple of days to get the extra unicorn as a way of preventing an innocent mistake from becoming a major PR debacle. Clearly they didn't want to pursue that route, or even let the original fast shoppers keep their bonus alicorn. They decided that only allowing 1 earned alicorn was more important than upsetting their customers.
Now that would not have been my preference, but if that's the path you are going to pursue, then it should at least have been handled respectfully. TL could have immediately put out a notice that any free alicorns would be removed from the game within a few days (I assume the delay was for time for programming the Ali-napping). Would people have been disappointed? Sure. Would people feel betrayed? Probably not. The lack of communication made an unfortunate situation into an egregious one, in my opinion.