Here's another good reason to question whether this was a principled move: once upon a time, in October 1999, Senate Republicans led by Phil Gramm were deep in negotiations on key legislation to deregulate the banking industry. The New York Times reported at the time:
"The deal was announced about 2 A.M. after a compromise was reached over the measure's effect on lending rules for the disadvantaged, the source of months of partisan bickering between the White House and Senator Phil Gramm, the Texas Republican who heads the banking committee. ... For more than 20 years, Congress has tried unsuccessfully to rewrite the nation's financial services laws and repeal Glass-Steagall... That all changed in recent years as the lines between the industries began to blur and it became more broadly acknowledged that a deregulation of financial services could be beneficial to insurers, bankers and securities firms alike. Once the three industries rallied around the legislation, they became a formidable political force, raising millions of dollars for lawmakers and pressing both Republican leaders in Congress and the White House for new legislation."
Those negotiations took place on October 22. And where was McCain at the time? At a presidential debate in New Hampshire, praising deregulation. Take a look for yourself:
McCain's quote: "There's a number of reasons why we are experiencing this almost unprecedented prosperity. Among them are a lack of regulation, free trade, and most importantly, we are going through a revolution the likes of which the world has seldom seen."