Willie, the original quote probably refers indeed to a criminal activity - armed robbery - being compared to the unwary being ripped off by legal contracts all drawn up by lawyers and 'sold' to them by slick salesmen. Woody Guthrie was turning Pretty Boy Floyd into a Robin Hood figure and camparing him indeed to the bankers and the big land owners.
My son, aged 18 and at university, was sold such a slick package quite legally by his bank when he opened a students' account: for monthly fee he could insure his belongings (they are already covered by our house insurance), join the AA (he doesn't have a car) and several other items he neither needed nor wanted. The salesperson made a small fee for herself and this was her only consideration rather than what was in my son's best interest. But he accepted this offer because it was from a bank and, because of his inexperience, he trusted banks so it must have been good.
Of course it is nowhere near as traumatic to be ripped off by a bank as being robbed at gun point but the financial result may be well have been the same.
What is or isn't legal has nothing to do with what is morally right or wrong - and the rich and powerful make the laws, as has been pointed out above. The cheating MP robbed us of peanuts compared with the vast bankers' bonuses. Where is the greatest evil?
The small time builder 'backpockets' the £100 cash he was given for a job, doesn't declare it to the Revenue and commits the offence of tax evasion. A very rich man transfers a few million pounds to his wife who is resident in a tax haven so avoids tax quite legally. Where's the greatest evil?
Of course the big bonuses are taxed (we think) and the rich man employs a lot of people. But do we really want to live it a society which tolerates such behaviour because the rich incidentally do some good. As was said above there are very few rich people in prison.
Perhaps I'm being cynical in wondering if our masters in making an example of a few cheating and quite dispensible MP's were an attempt to divert out attention from the bankers.