What sorts of people wear them?
Skate kids, Hip-hop heads, Muslims, Christians, Atheists , Socialists, Pacifists, anti-war protestors, anti-racism activists, various boycott movements and conscious objectors.
The designs mean different things to different people, plus the context can completely change many of the meanings:
If a white-guy wears a Malcolm-X t-shirt, then he's a sincere decent bloke. But hold up a minute – if a black-guy does, then he could be seen as some pro-black supremacist, who thinks that the white-man is the devil!
Equally, If a Muslim with a beard wears the Malcolm-X ‘by any means’ design, people may wanna clutch their handbags, call security and get him kicked off the subway. But if some skate dude has one on – he's cool, witty and anti-establishment.
Same with the ‘Jesus is a Palestinian' design – it's aye okay for any non-Muslim or non-Arab to express their support for the Palestinians and not be branded a threat to society.
If you think about it, it’s amazing that someone like ‘Che’ has been allowed to become probably the icon of all icons on t-shirts; considering what he’s said and done.