I agree with Slowmover. Perhaps it is because I live in one of those "hazards only when stopped for hazards" states, but when I'm driving in heavy rain and/or fog and I come upon those flashing red lights, I'm kind of alarmed because:
1. Visibility is often so poor that it's often hard to just stay centered in my lane on the highway.
2. When vehicles pull off to wait out the conditions, they usually put on those four-way hazard flashers and that's what I'm conditioned to expect.
3. When I approach those flashers dead ahead of me, I ask myself: am I properly in the lane and just approaching a vehicle going really slow with their hazards on, or have I drifted off to the side and about to cream a stopped vehicle waiting out the conditions?
That's why I don't like the hazards activated on a vehicle while it's underway, with the possible exception of a mountain grade. But then, on a mountain grade, I'm naturally alerted to traffic with more varied speed than normal anyway.