It makes it more likely that it was an official mall policy. (It might not have been though - it could have just been multiple incidents with the same security guard.) And he knew that without an incident that it wouldn't change. So he was willing to get arrested to make a point.

Doesn't change the fact that I don't like the idea of store owners deciding that their customers should not wear what is really a pretty blase t-shirt.

I am glad that he made the point. Even if I wouldn't have chosen to.

Cheers,
Ben