My point is the government stepped in and changed the regulation, which capped the banks ability to charge a fee. Instead of losing that revenue stream, they passed it on to the consumers directly. A bank's profitability, or investment history has nothing to do with that behavior. Any institution would do the same regardless of their financial health. If the government stops one revenue stream, they will open another typically against the consumer.
I understand what you are saying, but I don't necessarily agree. I would rephrase it as
"Instead of losing that revenue stream, they will consider passing it on to the consumers directly." [bolding is my change].
Yes, the company will want to make up that lost revenue stream. But they will also consider how much goodwill will they lose, and how much revenue they will lose by losing customers (for example moving their mortgages to credit unions). If a bank's back is against the wall, they may decide they need the short-term revenue stream in order to survive - and they'll worry about the long-term potential loss of customers later when they have some more room to breath.
Banks that are financially healthy have the luxury of being able to think long-term. And losing customers over a monthly debit card fee will seriously erode your long-term revenue streams, like mortgage interest, credit card interest, etc etc. Plus, if your competition is healthy, they can (and will) use the fact that they don't charge a fee in order to steal your customers.
It doesn't help matters that in the US, I doubt that many banks are making any money at all on their mortgage portfolios. They need this revenue stream. My argument is that if they had been regulated at the beginning, and couldn't get into the sub-prime market, then the debit card revenue wouldn't have been quite to critical. Charging this fee, to my mind, shows just how desperate the banks are to stay afloat.