the short answer is this:

you pay SS tax up to a given dollar amount, you also receive benefits based on a formula that involves the amount you pay in startign most recently and for some years prior to that.

what BHO is proposing is to disassociate the tie in between what you pay and what you draw. So where you pay only up to around 100K now and get benefits relative to that, he would have people pay the percentage against whatever they make but cut off the benefit relative to the pay in.

and if you think that "progressive" income tax was disproportionate, you aint seen NOTHING !