Of course at your age, and even well into my late 20s I'd have ranted against any uniform dress code as unnecessary authoritarianism. But having reached a state of wisdom myself, I now understand that it is not the message on the shirt, but the distraction it can cause, that matters to grown-ups (i.e., the ones actually funding the education). While I still think marijuana (along with other drugs, all gambling, prostitution, etc.) should be legal, I do not want our school students to continue to lag behind the students in other OECD countries in mathematics preparation, etc. I think removal of distractions, political, sexual, or otherwise, is appropriate. In fact, an appropriate school uniform should be baggy, white, and cover the entire body except for the eyes and hands, which are needed for performing the schoolwork and laboratory exercises.
I think you missed the qualification of my statement in which I said "unless the shirt is structured to somehow create a tangible disruption to classes...".
Or, perhaps you simply felt that you agreed with me so much that you'd write an entire paragraph about it.