In theory they shouldn’t glare oncoming traffic, but in practice many fog lights
Oncoming traffic aside, they can actually be detrimental to your own ability to see farther at night. Fog lights increase foreground lighting which seems brighter to our brains because more light is being reflected back to our eyes. But that increased foreground lighting makes your eyes adjust to the increased light and constricts your pupils more, thereby reducing your ability to see as farther away at night. Foreground lightning is unnecessary in clear conditions at speed.