[maconic]

From an ethical perspective, I think it just depends on how you will use the leads. If you make sure you're giving the leads to a scrupulous company who will offer the customer a valuable service that (s)he was looking for, then I don't see any ethical problem there.

From a business perspective, I think you'd need to figure out who would buy the leads after you've generated them. Perhaps you should start by coming up with a niche with a dearth of lead generators, find a company targeting that niche, and ask them if they would be interested in buying leads. By ensuring there is "customer" for your leads you can save yourself wasted time. Customer development (a la Steve Blank) for lead generation, so to speak ;)