Salt is a deadly poison. The question is how much. Which is precisely why Midgely would demonstrate the "safety" of TEL by pouring some on his skin in front of reporters. He knew that in limited amounts the effect was small.

At the time when TEL was introduced gasoline engines were just _starting_ to be mass produced for personal vehicles. It was a way to take the limited manufacturing technology of the time and still produce a reliable engine. The installed base was small enough that if you didn't consider the potential exponential explosion of engines you might be convinced that it would never amount to a significant problem. Sure, it will increase lead levels, but hopefully not by that much.

Then two world wars broke out. Wars in which this technology featured significantly.

It's fun to blame Thomas Midgely for all of this but if offers no real lesson on how to prevent it from happening again.