Well, I don't see it so much as caring far too much about cupcakes as someone diminishing/devaluing the care/effort I expended doing something that I did out of love (a little like the poster in another thread whose DH, upon being presented with a robe lovingly crafted overnight by the poster for his birthday said, "Well, it's not a real present because it's homemade"). Oopsie didn't just pick up generic cupcakes at the grocery store, she made them, and she didn't just make them, she took the time to figure out a cute design, get the supplies, execute them and then bring them to the gathering. BIL and DH diminished all that with BIL's antics and DH brushing off what he did (I had to explain this to my own DH when he just couldn't understand why I want nothing to do with his so-called friend).
They weren't just cupcakes; to me, they were a representation of Oopsie's love (unless Oopsie made them for money, which Oopsie did not indicate she did).
Also, would it change the issue if Oopsie had spent even more money for a bakery to make them just for BIL to ruin them, which is what he did. They were decorated to look like baskets, and he ruined the effect by picking off the handles.