Or is speech only meaningful if you added it to your shopping cart and it went through the pipes of commerce? Kind of exactly what people are upset about in the first place?
You're being a little pointedly obtuse here. People want the world to reflect their values. Very few political vegans would prefer to ignore that there are still restaurants serving meat, they'd rather the culture shift away from that sort of practice. Similarly, people would prefer the sport they enjoy watching not support the government policies they don't support.
"Why not just ignore anything you don't like" isn't how the world works.
It’s a shirt. You’re not using the brand. The manufacturer of the shirt is. You have no licence. You own property. You can deface it however you see fit.