Is the absurdity the charge or the statute though? Why is there a law on the books that allows them to be charged for glitter?

The answer is because an over-reactive police force encountering an "unknown substance" may end up spending significant resources shutting down the area and checking it for chemical and biological weapons, and nobody wants them to do that but neither does anybody want to be seen blaming the police for being overly cautious, so the blame is assigned to anyone giving them an excuse to do it. And then the police and prosecutors are given another weapon to use against harmless protestors that amounts yet again to felony causing trouble for the establishment.

The problem is the system rather than the people. "Punish the prosecutors" is trying to cure the disease with more of the disease.