Final Destination caused an entire generation of drivers to abjectly refuse to take up any space within a quarter mile behind a log truck.

First thing that came to mind is Upton Sinclair's The Jungle which led to, among other things, the creation of the FDA.

That wasn't his goal though; he's quoted as saying: "I aimed at the public's heart, and by accident I hit it in the stomach."

Star Trek introduced a lot of the first concepts of what we currently use as every day technology, it had a first hand tangible impact on the lives of pretty much every human alive today.

The Hindenburg crash. If it weren't for the newsreel, it would have been a unique airship crash and the airships would have continued to fly. But because it was shown in every theater as a newsreel for months, the interest in airship travel tanked and fleets were dismantled. It was actually a safe form of travel for the time. While tragic, only 35 people actually died, which is peanuts to a large air liner crash.

(Personal case, but i think i am not alone) I have been interested in science since Carl Sagan's Cosmos, i was a kid when it aired.

Dracula and Frankenstein both came out during the same year, 1931. Dracula was so popular in early 1931 that they were able to do all of Frankenstein by the end of the year. Can you imagine?

Those two began the modern era of horror. Modern being not silent.

The book Unsafe at Any Speed was partly responsible for the formation of both the US Department of Transportation and the National Highway Traffic Safety Administration.

Anime causes rise in invasive raccoon population in Japan

How about war of the worlds radio broadcast?

https://en.wikipedia.org/wiki/The_War_of_the_Worlds_(1938_radio_drama)

Jurassic Park caused a lot more kids to be interested in growing up to be paleantologists. Ironically, they went on to prove some of the science in the movie wrong

The Jungle was a book about the meat packing industry in 1906. It detailed horrific treatment of the animals and disgusting unsanitary treatment of the meat products.

It led to public outrage and caused the Meat Inspection Act to be passed in the same year. That Act laid the foundation for modern health inspections in food facilities.

The Apprentice 😕

Somwhow, no one has mentioned Lord of the Rings, which basically invented modern fantasy.

The first Federal laws against hacking and computer crimes was a direct reaction to the movie War Games (1983).

From Wikipedia:

President Ronald Reagan, a family friend of Lasker's, watched the film and discussed the plot with members of Congress, his advisers, and the Joint Chiefs of Staff. Reagan ordered a full national security review. Within a week, the Joint Chiefs of Staff returned an answer: "Yes, the premise was technically possible". Reagan's interest in the film is credited with leading to the enactment 18 months later of NSDD-145, the first Presidential directive on computer security.

A single piece of media, then Neuromancer, but really it's the entire cyberpunk literary subgenre of the 1980's and 90's, including the Cyberpunk TTRPG.

The first weekend of Pokemon Go was the closest we ever got to world peace.

The 24 hour news cycle. It made the news dependent on ratings and turned into an entertainment medium to fill all of the extra hours. Before that, it was a half hour of local news and a half hour of national news at dinner time and at bedtime with snippets of news in the morning on things like the Today Show. CNN created a format, Fox added imaginary outrage, and things went downhill from there.

I'm not claiming to fully understand the cultural impact, but I've heard from native Irish folks that Zombie had a material impact on The Troubles.

It's also a banger.

I'd probably rank the Bible as having the largest impact. It was both widely disseminated and had a large social impact in a number of areas.

Silent Spring helped kick off a number of environmental policies in the US and elsewhere.

The Exorcist bears some (much?) responsibility for kicking off the Satanic panic.

Many war photos could work for this question, too. The first one that comes to mind for me is "The Terror of War," often called "Napalm Girl," from the Vietnam War.

I would argue that Rainman (1988) being a lot of people's first introduction to autism propped up the autistic savant trope

Hackers (1995) did not reflect reality at all, and entirely made up a look, sound and feel of hacker culture for the film. Tech press largely panned it as rediculous, unrealistic and innaccurate, but hacker culture actually morphed into something close to what was depicted in that film because it's honestly way cooler and way better than what the actual hacker culture was at the time

Others have already pointed out really good examples like Upton Sinclair's book The Jungle which spawned a lot of food safety laws, or Wargames (1983) basically prompting the Computer Fraud and Abuse Act

Edit to add: I also remembered another very influenctial author at the turn of the century was Henry George who wrote a now under-discussed book called Progress and Poverty which is widely credited for triggering the beginning of the Progressive Era

In a similar vein, Charles Darwin's On the Origin of Species basically kicked off the entire field of biology with the scientific theory of evolution

Some of the early science fiction novels had real impact by providing plausible guiding lights for actual scientists about which directions to go in their pursuit of technological advancements. It’s been said that the first step in innovation is imagination, not actual scientific progress.

Ronnie James Dio and his devil horns hand gesture. It became a symbol for rock and metal music, but people often use it as well for other meanings too.

Surprised the Crying Indian American TV ad isn't in here. I have a giggle when I see someone on here outraged that they saw someone toss trash out their car window. That was SOP until the Crying Indian. I can't think of a PSA in my lifetime that made such a dramatic impact.

While not a piece of media exactly, reporting on the Tylenol Murders changed packaging almost overnight. Used to be you could pull anything off the shelf, open it and close it, no one would be the wiser. I remember as a kid suddenly encountering all the things suddenly having tamper-proof packaging. It was truly wild to my young brain.

Metallica held a concert in Russia and two weeks later communism fell.