Most self-made rich people get there by (I'll bet you've heard this before...) making something people want. It's a rare buyer who buys something for $20 and values it at exactly $20 -- most buyers think it's worth a little more, or a lot more. That difference means that most purchases are not only beneficial to the maker/inventor (who is making money on the transaction), but also to the buyer (who believes their life will be better because of the transaction).

So, if you set everything else equal (purchase of goods and services, payment of taxes, etc.) the self-made rich are doing a lot more for others than the rich-by-inheritance.