The solution, whatever it is, does not include anyone continuing to pretend that the SSN is now or has ever been suitable for any purposes other than for tracking government benefits managed by the SSA, and possibly also for tax filings with the IRS.
... and all of the other government benefits, programs, or mandated activities, many (all?) of which demand your SSN. Are you even sure that the credit industry, i.e. banks, originally misused SSNs? I wouldn't be surprised if they were required, by the government, to use them, precisely because it is the closest thing to an official "unique identifier".
Some people also might be concerned with not receiving their SS benefits either, which isn't entirely far-fetched given that others might now be using it for nefarious purposes (like trying to collect their SS benefits).
I read something somewhere else (maybe on a different HN thread, maybe here?) that this was changed in 2000 for something called "red flag laws", IIRC.
So yeah - it is required.