Perhaps the 9 year old child laborer would otherwise starve. I'll gladly buy the T-shirt every time.
Or think of it like this. If all T-Shirts were required to be made in the US by union laborers working 30 hours per week and each one cost $50, I'd probably buy a heck of a lot less T shirts.
I don't understand why necessity even comes into this. We don't need a lot of things. We don't need freedom of speech. We don't need more than 2 pairs of underwear or a car either. I don't need more than 2500 calories but I like being able to go eat a big juicy $50 steak sometimes. In the US it's actually illegal to go faster than 65 mph (75 in some awesome places) so why should we make cars that go faster than that if you obviously don't need it.
If you don't need the stuff you are currently buying there's nothing stopping you from living in a 4ft high hole in the dirt and eating cereal with water instead of milk and only buying locally produced goods.
Forcing someone else to live up to your definition of necessity is a pretty shitty thing to do though IMO.
Tangent: parts of Utah and Texas have speed limits of 80-85 mph. Their speed limit laws are also prima facie, which means you can get out of a speeding ticket by proving your speed was "reasonable and prudent" even if it was in excess of the limit.
Or think of it like this. If all T-Shirts were required to be made in the US by union laborers working 30 hours per week and each one cost $50, I'd probably buy a heck of a lot less T shirts.