|John A. Bird, Founder of The Big Issue|
Personally, I don't know anyone who buys it out of anything but sympathy for the seller. Buying The Big Issue is an act of kindness, like giving money to a beggar or that glorified beggar, the busker.
You don't hand over the money because you like what you've received. You do it because you know that acts of kindness like that are what makes the world go round. The founder did quite well out of it though, didn't he? It all rather reminds me of the slave trade.