There is no difference if the bonds Treasury "hands over" to SS aren't "the same" as those you might buy on the market. It's the same damn thing - money borrowed, money owed. The fact that it's a contract with SS and the American people doesn't make a bit of difference when compared to the obligations on bonds sold to China and the sovereign funds.
Treasury might, in some alternate universe, default on those bonds it sells on the open market, but what's the solution if they can't afford to pay them back and choose not to default? Raised taxes, increased revenues and "austerity measures". Then WE (the bottom 99%) still pay for it. So they're going after OUR money instead, via the debt owed to SS - money we all paid into SS over our working lives - to decrease the national debt, for the short-term, to improve the balance sheet and justify the excuses for continued, undeserved tax breaks for those at the top of the heap.
The whole thing is one huge lie, a scam on a previously undreamed of scale to continue to defraud the American public. They had a plan, and it's coming to fruition. There is, and never was, a "crisis" in SS funding. The crisis was contrived to provide an continuing excuse for tax breaks to the wealthy and corporations ON OUR BACKS, then to hand them even more of OUR money via a default on Treasury bonds due to SS.
I'm sorry if you don't get it, but this is a useless argument. The facts are clear: We're getting screwed so the top 1% can continue the kleptocracy in one of the most transparent examples of "The Shock Doctrine" ever attempted.
It's not a crisis, it's a scam and it's theft. No how, no way those who contributed to SS over their working lives should allow our government to default on those bonds so individuals and corporations who pay far less of a percentage in taxes than the average middle class worker can continue paying less in taxes.
They simply want to default on SS (at least a portion of it), to justify continuing on our unsustainable path. The answer to this artificial crisis is "austerity" and higher taxes for the top earners and corporations - the same corporations sitting on $$$$ about equal to the the debt owed to SS.
Funny how that worked out.