Exactly

Discrimination against people that are not defined by law to be a protected class is 100% legal.

For example, cigarette smokers are not a protected class, and in some places, they are hated as much as peds. An employer can fire someone who smokes in their own home on their own time, and declare the reason for termination is that he simply hates smokers and thinks they are vermin. Nothing can be legally done about it. You could have Facebook groups that call for the extermination of smokers as well. Businesses can refuse to sell goods or services to smokers. No law against that.

Years ago there was discrimination against families with young children in the real estate business. Landlords wouldn't rent to anyone with kids because they'd trash the place. Have kids? Don't bother applying. We don't want you here. Now they're on the list so landlords can't refuse to rent or sell a property solely for that reason. In realtor class, we were taught specifically who we could and could not discriminate against.