I am disspointed by the elitist attitudes in this thread.
I get that maybe you (geneal you) don't want used underwear, but as a PP pointed out it really isn't actaully, from a germ/sanitation standpoint, much different than eating off of plates and with cutlery that others have used when dining out, sleeping in a bed made with sheets others have slept on at a hotel, etc.
If it skeevs you out perosnally, fine, don't do it. Lots of people have issues with whatever thing. Me? I am skeeved out by people letting their dogs lick their faces---I could never do that. But to look down upon others who aren't skeeved out by it is just so wrong (whether the person could afford new undies or not--who cares? Honestly, if you stop the stupid stigma about how gross it is and only ok if one has no other choice, then it will be much less awful to not get to make the choice, than if someone feels so totally judged for their poverty).