Here's an interesting thought. Though....not a new one....
One of the reasons the first Jaws movie was so fantastic is because it touches on an aspect of group mentality concerning a disaster... "This isn't really happening....we can go about our business." Or, "the idea of this possibly catastrophe being real is something that threatens our very survival, so we look for altering theories (a boating accident) to convince us that this isn't really happening."
So with Yellowstone, and I believe this is a very fair question...do you personally believe that if there was a very real threat of Yellowstone exploding, and the fallout was going to basically kill half the US, and there was no way anyone had the resources for an evacuation of that magnitude... Is it wiser to NOT tell people? Not cause a panic? Not put every west coast major metropolis into complete anarchy?