I drove through once; my feeling is that it takes a fair amount of guts to live in the desert-that desert, in the summertime. 120F+ is lethal to the unprepared who are out in in it for more than a brief period.
If you look at the Wikipedia climate tables for Slab City and Tempe, they're basically identical.
You're correct that it's lethal if you're unprepared, but so are plenty of other places and temperatures at both ends of the spectrum. I wouldn't want to sleep without AC in that kind of heat. But humans have survived temperatures like that for all of history.
That's not to say its _easy_ and without AC it can be uncomfortable. But you can survive. If you have an RV, fans, perhaps a make shift swamp cooler, and tin foil on the windows could get the internal temp down below 80 pretty easily.
Generally speaking anything over 100 degrees can be dangerous to the under prepared. At 110 degrees direct sun exposure can be lethal if you are not drinking approx. a quart of water per hour of exposure. But it _all_ comes down to exposure. Shelter changes the entire game.
I grew up in Israel and 40c (104F) was an unusually hot summer day (you'd get a few days like that per summer, maybe more now due to climate change). More common summer highs were around 30-35c.
EDIT: I underestimated how much hotter the Arabian Peninsula is compared to the Levant - a quick look via google maps puts Doha at 39c right now (at 9am!), while Jerusalem, Damascus & Cairo are at 22c, 24c and 27c respectively!
If you grow up in the area surrounded by people who know the area, you'll do fine.
If you're casually wandering into an area like that coming from San Francisco or London expecting a fun weekend, you may very well pass out or worse.
Have you never been outside in 120F+ temps?
I have spent many years of my life in those temps (Australia, all around Africa). Shade and plenty of drinking water and it's completely fine. Millions of people live their lives in those temps with no AC, no fridge, etc.
I hear the same thing about the cold like "Frostbite in a matter of seconds past -30F". I used to regularly ride my bike to work at -48C (-54.5F) and enjoyed it. With the right layers it was completely fine. By the time I got to work I would take off my jacket, gloves and touque and stand outside with a ton of exposed skin for 2-5 minutes in attempt to cool down. (though my legs were usually numb because I couldn't be bothered wearing more layers)
Please go out and explore and enjoy the world rather than fearing it.
Doing that without having sufficient warm clothes or a warm space nearby is very dangerous, because once you've radiated all your stored heat, you will freeze to death.
Likewise, 120F is totally fine if you're well hydrated and in a dry environment.
If you're dehydrated or it's humid, you will die. The wet-bulb temperature that will kill a human being is just 95F.
You SHOULD fear extreme temperatures - if you don't treat them with respect and make sure you're prepared, it's very easy to end up in a terrible situation.
The reference, the hottest recorded temperature in Australia is 123.2F (50.7c).
Yes it gets into the 40s pretty regularly in a lot of places in Australia. But even 45c in a heatwave is very different to “regularly” living with temperatures close to 50c.
I don't think I've ever experienced 120F (~49c). I guess I wouldn't be worried about dying personally, but I definitely wouldn't want to be outside for too long. Older people though? That probably is potentially fatal.
As noted, the occasional 45 C heatwave for a few days is pretty much peak heat so far with anything approaching 48 C | 120 F being a rare event.