Of course you COULD politicize his t-shirt...but that is your choice. Murder doesn't have to be about politics, it could be about a young citizen caring about the fact that there are changes that need to be made in society.
US News had an in depth article about this topic last September. A telling quote, "The vast majority of homicide victims are killed by people of their own race. People tend to kill who they know." If calling attention to stopping murder upsets you...I just don't know what.
full article worth the read here.