She first spoke with her employees, who disagreed with Sanders' defense of Trump's discriminatory ban on transgender Americans who want to serve in the military and her recent defense of Trump's un-American family separation policy.
In response, she then asked Sanders to step outside to the patio and "explained that the restaurant has certain standards that I feel it has to uphold, such as honesty, and compassion, and cooperation." Clearly, Sanders doesn't comply with that standard
As a progressive, I feel that denying service to a person is instinctively troubling. For many, it may conjure up laws that banned blacks from being served at restaurants before the Civil Rights Act and the current campaign by some on the right to turn away same-sex couples who want professional services for their weddings. Or even a gun range owner who declared that no Muslims were allowed on the premises.
But the situations with Sanders and even Nielsen are not even in the same universe as these discriminatory examples. No one is targeting them for their race, religion or sexual orientation.