First, the history of communist governments from the Soviet Union through China, Cambodia, Laos, and Vietnam shows conclusively that "Better Red than dead" wasn't an either/or proposition. Communist governments killed millions of their own people. They weren't exactly kind to those they conquered, either.

Second, the leading theory on the dinosaur extinction involves an impactor estimated at 10 kilometers in diameter hitting the Earth. That's a damned big rock and it released an unimaginable amount of energy. By way of comparison, this article calculates that if 1950 DA, an asteroid approximately 1 kilometer in diameter, struck the Earth, it would release approximately 60,000 megatons of energy virtually instantaneously.

How much energy would a 10 kilometer impactor release? It depends on several factors such as composition and impact velocity, but if all other factors were similar to the 1950 DA study, it'd certainly be more than 10 times as much. Asteroids aren't spherical, but to simplify, imagine they were. When you double the radius of a sphere, the volume increases by a factor of 8. The mass of the asteroid is directly proportional to the volume, and the impact energy is proportional to the mass. The volume of a sphere is equal to 4/3 PI r^3.

1950 DA
Radius ~ .5 km
Volume ~ .52 cubic kilometers

Dino Killer
Radius ~ 5 km
Volume ~ 524 cubic kilometers

The volume of the dino killer is over 1000 times that of 1950 DA. The energy released on impact would be at least that much greater assuming other factors like impact velocity and composition are similar. That's in the neighborhood of 60 MILLION megatons, a bad neighborhood indeed, and all released almost instantly in a single location. Nothing in human creation comes within a few orders of magnitude by comparison, even the combined arsenals of all sides of the Cold War. There simply is no realistic comparison between the dino killer impact and even the worst case nuclear war scenario.

And for the record, I'm very grateful we never had to find out just how bad a major nuclear war would've been. Without a doubt, it would've been the worst disaster in human history even without Sagan's exaggerations.