...Lester take the cup for stupidity...
I didn't see him as stupid at all. I thought his framing of his brother was pretty brilliantly executed, and his sending his 2nd wife to the slaughter was dark and despicable, but still a brilliant stab at self-preservation. He even disposed of the first wife's body pretty cleverly.
Giving in to your base instincts and smacking your wife with a hammer is not stupid, just not a good idea and not well thought out. But that is a crime of passion, a loss of control, which has little to do with how stupid one might be. There are lots of smart folks who lose control, and lots of stupid folks who never do.
We evolved from our less-endowed predecessors with tiny, undeveloped brains, which is why the construction of our current brains is a reptile brain connected to the spinal cord, with a higher-functioning brain wrapped around that. Our lizard brain is the only thing that connects directly to what our actions will be. Our higher brain is supposed to be in control by virtue of it keeping the lizard brain in line, but the higher brain is not connected directly to how we react physically or even emotionally; it hopefully keeps the lizard brain in line in a sort of fly-by-wire method, but if it loses control of that it has no capacity to stop whatever the lizard brain has in mind.
That is why I recommend against Ambien, because Ambien puts your higher brain to sleep. But if your lizard brain wakes up early and your higher brain doesn't, all bets are off in what you might do, because now you are thinking like a reptile with no one to tell you not to. There are scores of horror stories on the internet of folks who took Ambien and ended up peeing in intersections in their underwear, driving the wrong way on a freeway at 110 MPH, and yes, even smacking their spouse with a hammer.
Ask Patrick Kennedy, or a number of other high-placed folks who are on record as having problems with acting out after taking Ambien. I only know this because I researched it due to the fact that I lived it once upon a time, and I was lucky that my reptile brain did not do stupider stuff than it did, because when something like this happens, you are still responsible for the consequences. I skated, but just barely, and it was a hard lesson well-learned which affects me to this day.
Under the right circumstances, anyone is capable of anything. So a crime of passion is just that, and has different legal consequences than a planned crime, and little to do with any level of stupidity.
He also made some bad choices in Las Vegas, which if he had not, he would have got away scott free. But even non-stupid people can make bad choices. Of course they often don't have as dire of consequences as the choices Lester made.
No, Lester was actually pretty intelligent. But intelligence usually doesn't help matters all that much when you are panicked and running from the law, and Lester had been doing that for almost all of the series, other than the year break in the middle where it looked like he had pulled this off.
If Lester had just been stupid, it would have been a stupid show about a stupid guy doing stupid things. Instead, it was about an intelligent guy giving in to pressure, making bad decisions based on delusions of grandeur, and running for his life from the law and the mob and a hit man using whatever wiles he could muster up, which is exactly why the show was also not stupid.