Intuitively it seems very difficult to see how things could go all the way towards being Venus-like if all the positive feedback mechanisms kick off. We're really, really similar to Venus, but Earth's crust wouldn't appear to have that many greenhouse chemicals stored up. (Unless geologists have failed to account for something)

But there's a long distance between Venusian hellscape (hot enough to melt lead and raining sulfuric acid) and what we have today, and most of it is pretty awful for us. "Kill everybody" isn't crazy.