IMO a lot of it comes down to player expectations. If you say up front "player characters can and will die if they make poor choices or even just get unlucky" and your players sign off on that, you can put death traps and over-leveled monsters all over the place.

If you plan to run a high-lethality campaign I'd recommend having each player play 2 characters, with 2 backup characters ready to go. I call those meatgrinder campaigns.