No, it's not redistributive merely like fire or flood insurance. My $300,000 house will cost the same amount to insure as my similarly-housed neighbor who makes twice as much. And the additional cost to insure a $400,000 house isn't typically greater than the reduction in cost to insure a $200,000 house.
That's not how social security works. The benefit curve drops off dramatically in relation to the "pay-in" curve:
http://www.ssa.gov/oact/COLA/piaformula.html
And again, things will get worse when, seemingly inevitably, the payroll tax cap is lifted without substantially modifying the "bend points". A dollar you contribute to SS on your earnings over $56,000 is worth half the benefits of a dollar contributed under that amount.
The flaw that exists in the current discourse regarding Social Security is that the program is framed as a retirement program. It is not. It is "end of life insurance". In fact, one correct term to use in describing programs such as Social Security is "Social Insurance":
http://en.wikipedia.org/wiki/Social_insurance