If all people in the country suddenly closed their bank accounts and moved their money to credit unions, if EVERYONE suddenly did this, we would put a serious dent in the too-big-to-fail banks, as well as send a message. The difference between a bank and a credit union: with a credit union one is not a client but a shareholder, and therefore pays no fees. This is already a good reason by itself to move from a bank. Win-Win!
Why is this important?
It is important because right now Americans feel helpless in the workings of the government, disgusted. There seems to be nothing we can do besides rally behind Trump's traveling circus. On the other hand, this simple grass-roots action is one where the American people hold the cards.