http://en.wikipedia.org/wiki/Amancio_Ortega_Gaona
What did he do that was "illicit" (he certainly didn't inherit wealth as he started working in his early teens)?
I'm not sure what to make of the allegations of them keeping workers captive. But assuming the work is voluntary, sweatshops are not all bad. In fact, they're the fastest way we have to bootstrap an industrial economy in a developing nation.
Yes, these factories have terrible work conditions by modern, western standards. But compared to other local job opportunities, the factories are an abundant source of relatively well paying employment.
I say 'relatively well paying' because, despite how poor the pay is, the alternatives in the local economy are worse. Often, a so-called 'sweatshop' pays at least 2-3x the average local pay. It's almost axiomatic that a person would not work in a sweatshop if they didn't think the pay was worth it. So if they have workers in their factories, then it must be worthwhile to them. (That's assuming, of course, the work is voluntary.)
Once enough factories have appeared so that they have absorbed the excess labour capacity of the local population, the wages start to rise as the factories need to compete for the available labour. They also compete on non-monetary terms, through better working conditions.
Wages will stop rising when it becomes economical for foreign companies to move production to a cheaper place (after expenses related to building an entirely new supply chain there). If that starts to happen, then excess production capacity appears, which gets absorbed by local companies. At that point, the bootstrapping is complete and you have a self-sustaining industrial economy.
Over the past 60-70 years we've seen goods (clothes being a good example because it's labour intensive and not particularly capital intensive) being produced in a succession of countries. In no particular order, China, Hong Kong, South Korea, Taiwan, Singapore and Vietnam have all had their day as the primary producer of garments. Currently, they're made in places like Bangladesh and Sri Lanka.
So I don't consider sweatshops to be a bad thing in and of themselves. But they are breeding grounds for all sorts of abuse (including but by no means not limited to confining workers to the factories), which is a problem. So we should be pressuring corporations to ensure safe and non-abusive work conditions in their factories. We should not be discouraging them from operating factories in low-cost-of-living locations, or trying to artificially increase wages.
Not to say he didn't also work his ass off and have a great deal of luck. Buffett doesn't seem like a bad guy at all. Seems like a very 'grandfatherly' type.