Well, personally I wouldn't have a problem with it if my ashes were stolen and eaten, because I would be dead... but I'm certain that my relatives would be shocked and it would give them grief, so I suppose by proxy I would have a problem.
Yes, rationally speaking, there's no reason why we should place importance on the remains of our dead, but that doesn't change the fact that we do place importance on the remains of our dead. Sic, you are by far no rational nihilist, and I am sure there are people or objects to which you attribute sentimental value far beyond any rationality... it's part of being human. I would have thought that anarchists would understand this human aspect to the situation... I can understand attacking the system, but this is just plain juvenile dickery. It's one thing to disrespect someone's views and beliefs, it's an entirely different thing to outright disrespect someone, especially someone who's not around to defend themselves.