Opioids can definitely cause death in high acute doses. Benzos on the other hand are hard to kill yourself on, but are well known to make you wish you were dead if you try to get off them.
GHB back when it was on the market as a supplement put dozens of people in the hospital after they consumed "tablespoons" of the stuff. But if you take enough it will probably kill you as well.
However, GHB is probably fine used occasionally for sleep in reasonable doses.
I'm of the opinion that screwing around with GABA A receptors is generally a bad idea. Benzos are normally strong positive allosteric modulators of the GABA A receptor at various sites. Occasionally they can either be strong or weak agonists of that receptor as well.
GHB primarily acts on the GHB receptor but is also a weak agonist at GABA B. My suspicion is that this is inherently less risky than acting as a PAM at GABA A. But, I'll admit that I don't have a lot to back that up with other than a long history of drugs that work on GABA A being enormously problematic - barbiturates, benzodiazepines, and z-drugs in particular.
As I've said numerous times - chronically taking almost any drug that works on neurotransmitter systems is probably a fool's errand due to the drive to homeostasis and the resulting tolerance. But put an exclamation point on that for anything that works on GABA A.