Is it really? It seems pretty widely accepted that the death penalty doesn’t deter crime, for example, which indicates that people (well, potential criminals, anyway) don’t see it as substantially worse than a lengthy prison term.

It's not about which is worse either though. The implicit calculation is: If I get caught, will the punishment deter me.

But (approximately) nobody commits a crime on the assumption they will get caught, so it pretty much doesn't matter what the punishment is. The way to move the needle is to change the assumption about getting caught. The closer that tends towards guaranteed, the less chance people will even make above calculation in the first place.

Yes, exactly. And my thinking for travel is much the same. I’m not traveling on the assumption that I will be falsely convicted of a crime while I’m there. The way to move the needle on my decision to travel is to change the assumption about being falsely convicted, not what will happen to me if I am. Thus, a man already in prison for years suddenly being sentenced to death doesn’t change my travel plans at all.

Or that risk evaluation doesn't generally play a big part in decisionmaking that leads to crimes punishable by death.

It's a fascinating point that the pro death penalty crowd universally ignores.

US violent crime has plunged over the last 40 years, and the murder rate has been chopped in half since 1980, all the while death sentences have declined to ~45-50 year lows (there has been roughly a 90% reduction in new death sentences since 1999). The dramatic plunge in new death sentences over two decades hasn't coincided with any uptick in the murder rate or violent crime.

The people who commit heinous crimes usually have psychological problems that cause them to have very low impulse control. They don't think their actions through very well, which is why they're in their position instead of some better and more legal lifestyle/career. So harsher punishments really don't deter them; they don't expect to get caught and aren't thinking about that when they commit the crime.

There's a theory that violent crime has plunged over the last 40 years because of leaded gasoline being phased out: the lead was in the air and environment and giving everyone low-level lead poisoning.