Properly aimed foglamps are not a problem to oncoming traffic. That said, most people mis-aim them, throwing the beam upwards to get noticed. This defeats the very purpose of foglamps, which is to send a sharply cut off beam along the road surface, well below the beam of regular headlamps.
The first foot or two above ground level typically has a higher temperature, which creates a less foggy zone that hugs the ground (the exception is the "tule fog" along the central valley in California, which forms right along the ground, rarely rising above 15-20 feet.)
The value of the foglamp is that it projects below the reflective fog, illuminating the road and any hazards on it, but not throwing much light up into the fog to be reflected back, blinding the driver. Aim them high, and this only ADDS to the reflection, making visibility worse.
While it is true that a wet surface reflects foglamps into oncoming drivers, the same is true for a dipped headlamp beam. However, the effect is usually minimized by the uneven road surface which breaks up the reflection, effectively diminishing the blinding effect.
HIDs are far worse than foglamps is this respect. The foglamps are so much dimmer than HIDs that I am inclinded to make the mod to employ them as DRLs and forget them in fog.
Flashing high beams at a driver who is using properly aimed foglamps is not only offensive, but it is dangerous since it may blind him and make him run into you!