I've been DM'ing for a couple decades now and I'm not afraid to kill a character who makes a truly stupid decision. I was running PotA for a group who greedily decided to give their weapons to the water cultists to have them enchanted. The water cultists cursed the items to create a sphere of water around the wielder on command. The whole party drowned in those spheres of water, and their bodies were eaten by the cultists' giant alligators.
However, I have to say I'm not fond of PC death. It grinds the game to a halt for the player(s), and then I have to figure out how to integrate the new character(s) into the game. I can do it, obviously, but why should I when often there are options other than death for showing the consequences of a PC's actions. In the game I'm currently running, most of the party fell prey to dark elf slavers and are laboring under magics that force them to obey their new masters. Things have been difficult because I now have a party that's split into three parts, but it's been a lot more interesting than "Oh, you died. Make new characters."
Ransoming the PCs back to a wealthy patron or ally is also a good option. So is simply taking all their stuff (yes, all their precious magic items, focuses, holy symbols and spellbooks too) and leaving them for dead in an inhospitable place; give them a chance to earn their survival and make a compelling story out of it.
Now, there are certainly times where the consequences should be death, just based on the nature of the foes being faced. Invade a dragon's lair and find yourself ill-prepared when you discover it's still there, it's probably going to kill and eat you. Invade a cult and get caught trying to bring the brainwashed prince back to his father, you might be kept captive for a later sacrifice (giving you a chance at a jailbreak, and meaning your death if you can't make a go of it).
Edit:
When I do kill a character, they usually stay dead. There are rare exceptions, but resurrection is very difficult in the homebrew setting I almost exclusively run. To get a soul back from the gods you have to give one in return. This means human(oid) sacrifice, and it means most resurrections are performed by those evil enough to kill an unwilling sacrifice. It also means good characters who want to perform a resurrection need to find someone willing to die for the cause. And that's not always easy.