You can hide these faces and they will be collected in the "Hidden People" section of the Peoples album.
What I would not do right now is to delete the faces circle.
When you enlarge a photo and enable "Show Face Names" in the View menu, you will see the unnamed faces overlaid on the photo. The circle has an "x" and when you click this, the face will be deleted. But there is a glitch. The album of this person will now show with a blank white thumbnail and is not fully deleted. I'd wait for a bug fix, before you delete faces this way.
For the time being, I'd simply hide the unwanted faces of strangers in a crowd.
https://help.apple.com/photos/mac/1.2/?lang=en#/phtad9d981ab
You can hide all photos of a person in the People album.
- Click People under Albums in the sidebar.
- Control-click the person, then choose Hide This Person.
The photos are hidden from the People album, but not removed from your library. To show a hidden person in the People album again, scroll down and click Show Hidden People, Control-click the person you want to show, then choose Unhide This Person.