Can banks just decide to not do business with you
Yes. That's how credit cards get cancelled and mortgages get foreclosed on. Don't you think the bank would just rather you paid them? Because that interest is how they make money.
No, because that is theft. As parent said: "with their property." The money in a bank isn't owned by the bank. It's owned by it's customers. If the bank decides not to do business with you, they must return your property.
There are also laws against discrimination because a business can't just do anything it wants with its property, like put up a sign that says "No Blacks or Jews".
Yes, because discrimination on the basis of race or religion is specifically banned. But it's that category that is banned, not discrimination as a whole. Nearly every business has a "right to refuse service" clause or sign. You ever know anybody to get thrown out of a place for being an asshole? Right to refuse service. You just can't refuse service because of age, disability, gender, race, national origin, or religion (among a few other things), but you absolutely can refuse service for nearly everything else. "We don't serve people who are rude." "We don't serve people who bounce checks." "We don't serve people who complain for petty reasons." "We don't serve people without shirt and shoes." "We don't allow food in here." "We don't allow children into R-rated movies."
You know the Soup Nazi? That is not illegal.
Businesses usually have little interest in refusing services in general because it's -- quite literally -- turning money away, but that doesn't mean they don't get to decide who they do business with.