Opportunities are not "given". I don't go to work thinking, "just look at all the opportunity I'm creating for other people by contributing to industrial civilization."
Rawls is wrong. The idea that "you didn't earn your brain, your family, your upbringing, etc." is completely in error because the concept "earn" only applies to situations where choice is involved. In reality, "earn" distinguishes the hardworking doctor or construction worker from a 30-year old man that won't get a job and still lives with his parents.
I say that if you make the most of what you've got, it doesn't matter if you started out with $5 or $5e7. What matters is that you make the most of the opportunities that are out there. What matters is how much you improve your lot.
I say that the purpose of morality is to have a happy life, here on earth. It sounds like you are against "enjoy yourself and live."
Edit: Here I give the answer to most of the people that are downvoting me. Clicking the down arrow to shut out other viewpoints won't help anyone get to the truth on the matter.
However, success in today's world is not driven solely by "creating value" for a variety of reasons. Don't succumb to the "just world" fallacy - it's easy to moralize about how the unsuccessful must be lazy, but applying a little bit of critical thinking should make it clear that a rural shepherd in a third world country isn't necessarily poor because he "chooses" not to work hard and become a surgeon. Indeed, well-targeted charity may increase the returns to hard work.
As a side note, it seems quite plausible to me that redistribution from the "lucky" to the "unlucky" will result in a growing pie for all, though perhaps it won't grow to the extent that the very lucky are better off than if the redistribution didn't happen.
By all means be a miser if that makes you feel better, but don't cloak your actions in "morality".