I would expect most would cite a thought process more akin to "I'm a safe driver, have never hit a pedestrian or cyclist before, and don't expect to in the future, either." for why they aren't swayed by this warning.

I expect very few went "I don't care about killing people with my car", for their reasoning.

Now, people are a terrible judge of their own talents at driving, and so many of those people are much less safe drivers than they think. But the point here is that most of those people believe they specifically are not at risk of causing that terrible outcome. It's faulty risk assessment rather than total lack of caring about others.

To be fair, the vast, vast majority of drivers will go their entire lives without hitting a pedestrian, let alone at speeds that are fatal. Where I live, pedestrians deaths seem to always be from drunk drivers, the very young or very old, and people walking across 20 lanes of interstate at night for some reason.