Look at it this way, do 2 wrongs make a right? If you choose not to pay back at least what you borrowed, are you any better than them? You are technically stealing the money like they are stealing money from people, and just because they are doing it, does it make it right for you to do the same thing?
You have to choose for yourself what you are going to do. You are the one that has to live with knowing that you stole that money and by not paying back at least what you borrowed, that is what you are doing.
This is how I feel about it, but again, it is your choice.