Yeah, I like insta death effects, but like you said, I control how much I use them. I definitely use them more often then you. I will often use them when it is the key encounter fo the current adventure.
Still, it depends. Like for me I also consider what level they are, have I had the opportunity for the PC's to make friends with high level NPC's yet? Plus I use luck rules (adapted from Unearthed Arcana) and the classic "God Call" to also mitigate the threat.
Still the threat is there, and so is the adrenaline rush of making such critical rolls. I would prefer the player suffer the effects of a successful roll, but the possibility of death is what makes the roll so adrenaline filled in the first place. So its a trade off I deal with.