Lots of good advice here from others.
I like Ben's 'don't be too scared' advice.
Being sensibly cautious is wise.
Question: Furthermore, he said that it is dangerous because you can't use the air condition in your car because it is too hot
We used air conditioning for several hours on as hot a Death Valley day as you are likely to ever get. It worked very well and was most welcome indeed.
Without it the trip would have been far far less bearable - you would want windows open and to keep moving when in the car.
Danger is minimal if you are sensible and do not drive or wander into places which are not well thought out. There appears to be enough traffic to make it likely you'd be discovered 'promptly enough' in any place that you'd sensible drive. This is not the Australian Outback - stay with the car if it dies (but it wont).
People ride bicycles and hike through it. Others (admittedly of questionable sanity :-)) run through the valley,
We received no advice about Death Valley being unsafe to drive in. The name suggests that you may want to take a little more care than in, say, Paradise Valley, but it's not especially risky if you are sensible. That word keeps cropping up. Do something really stupid there on one of it's hottest days and you'd find it easier to die than in many other places. Otherwise, it's safe enough.
Standard precautions apply: Fuel / Oil / Water in car checked. Good amount of spare water for you and car. Spare tyre in good order. Tow rope & jumper cables would be sensible to have (that word again) but I'd be sure to have them anywhere. A means of making shade would be exceedingly welcome if you did have to 'camp' for some hours. A standard plastic tarpaulin would do. Size to suit the amount of shade you'd like to have.
It's fine. It's fun. It's safe. Do it !!!
We spent a few hours there in midsummer around early to late afternoon on the then hottest year on record (2003). Temperature at the Furnace Creek store in mid to late afternoon was just over 50 C on what LOOKED to be an accurate and expensive circular thermometer outside the store.) An hour or so earlier we wandered around Bad Water and local weather station (then by cliff side - since moved) said 50+ AFAIR.
Stick to the roads when driving - gravel roads up to lookouts etc are fine. There is no great reason to not do so unless you have something specific in mind. You can see most of the core sites in a relatively straight forward path in a few hours. I imagine there will always be a steady trickle of cars on the mainer roads. A web search does not provide much hard evidence of a substantial death rate of sensible tourists Here is an incredibly extreme example where a child died after his mother drove far off road in obviously dangerous circumstances. You are not going to come near to doing this sort of thing.
Dante's view (an absolute must!) with one mile+ crop to Bad Water on what LOOKS like an easy down slope. Do not try it!!!. (I (stupidly) considered it.) Look at map. Work out mean fall angle. Wow. Must be cliffs down there somewhere. One mile+ view to Valley floor an views far into distance. . Impressive. Dante's view images
Zabriski Point (unrelated to the movie, it seems). DO NOT use the toilets by yourself. Do not shut the door. Really! :-). My wife did both - the arriving bikies persuaded her that shutting the door was wise. It wasn't. She thought she might die before she got the door open again.
DO NOT follow any apparent walking tracks. Odds are you can do so with ease and relative safety if you know what you are doing. You can even run ultramarathons up the valley if you know what you are doing! People do. Run on white lines when available. Keep N sets of shoes in freezer in support vehicle and swap them often. BUT people really have died just crossing the immensely interesting ridged mini hills near Zabriski point. "Take the car round and I'll see you over there in half an hour ...". Male. Young. Fit. Dead. Really. Probably an underlying medical condition to help it happen. But YMMnV.
Can stay out of car indefinitely up on top of ridge - 5500 feet above valley floor.
Badwater. MUST see Badwater. Take a big water bottle. Wear WIDE brimmed hat. Take a towel.
You do not sweat. Apparently. In practice you do. But the seat dries off the skin faster than it leaves your body leaving nice salty tasting skin. This is called dying. You can do it happily (if you are us) long enough to have fun, take photos, wander a few hundred metres out on the salt pan and feel like you are a hero. Ofdds are there will be advice that tells you how to manage day hikes there, but just being sensible seems to work fine for modest looking around.
Why the towel? ... Fancy that. Pools of water here in mid summer. Dips toes. Hey, that's hot. Dips finger. Licks. Ugh. Wow - that IS alkaline isn't it. Funny that, my foot is itching! Wet towel. Rapidly wipe foot to remove Alkalai. Retreat.
Lie on salt flats in turn and take pictures. Lots of fun.
Officially the hottest place on earth on a good day. A place in Algeria was in 1954? but since disqualified.
Dante's View view. Badwater about 5300 vertical feet below Carpark and met station hidden to left. Road along valley floor going right leads to Stove Pipe Wells, Amargosa, Lone Pine, sand-dunes etc.
Dante's View view from Dante's View page - Wikipedia - the full size version a superb 6400 x 18090 panorama view. Other excellent images on that page.
Image page here
Drive up highway from Vegas. Air Force base on right is where they control the Predator Drones from worldwide. Really. Nothing to see here. Move along.
As you come in from the road from Vegas, turning off somewhat before Area 51 (you'll see the signs) you find several interesting things.
Indian casino on left. Drive on by.
Amargosa Baptist Church (on left) just after Casino.
Stop and look briefly.
Photograph the sign, and the church, and both together.
If they are as they were 10 years ago then you will see why.
Proceed to Amargosa Opera House (!!!!) on right. Stop. Marvel. You may be lucky and get to see the inside.
Look it up. Fun.
Drive on very short distance to Amargosa hotel on right. Marvel. Big!. Web will tell you why. Same reason as Opera house existing. SPOILER FOR BOTH HERE When we arrived there was an immense puddle - really huge. And no people. At 45C or so. A mystery. Turns out they had had a water main break and hotel was evacuated due to lack of water. More fun not knowing why :-).
... Stovepipe Wells xxx miles
... Shoeshone xxx miles
John Wayne is gone. But you can feel the history - even if no Indians are in sight.
(See Casino, above).
Look for "Flash Floods" signs on creeks, and smile. At other seasons take care.
As you cross the Valley towards Stovepipe Wells you will see the famous sand dunes. Take photos. All angles. They look great afterwards. You will always regret not taking enough.
If you head for Lone Pine note the LARGE steel "radiator water' tanks every xx miles as you grind up the long long hill.
If you go to Lone Pine (next stop Mono Lake, then turn left to Yosemite) consider staying at "The Dow". Very run down hotel. Seen much better days. If you do not stay, see if they will let you go and see the "John Wayne slept here" plaque. Apparently his preferred staying place on many filming visits long ago. Or, so they say.