You do have the right to your opinion and feelings in this. If you do not see it....OK. I will not dispute you in that.
If I walked into a middle eastern business doing or wearing something offensive to them I would expect to be called out on it and I would be.
If this young fellow was doing this to offend he needs to be called out on it for the same reasons. As stated, I would ask what the shirt was about. How the discussion went from there would be up to him. That simple. If you could walk past and ignore it then good on you. Some of us could not. There is still some patriotic honor in some of us.
If you do not see "It" then I am wasting my time.
Again, your life, live it.
Do you blame the mujahideen for 9/11 ?