What is something that people think is dangerous but in reality is completely harmless?

Also double dipping in a sauce or dip.

Perhaps, but still gross.

George likes to double dip

Was this a technological change, or did gas stations just not want people loitering on their phones?

IIRC, the rate of explosions at gas stations started going up around the time that cell phones were becoming popular. The investigation teams would review camera footage and see people on their phones. So the government changed the mandatory warning stickers on the pumps to include a "do not use your phone while pumping" warning.
Turns out it wasn't because people were using their phones near the gas pump, but that they were getting back in their cars to play on their phone while the pump was running. They'd build up a static charge by getting in and out of the car, which would arc to the pump handle when they went to hang it up.
It took a while before they realized what the actual problem was.
- Interesting. Any sauce? Just curious why this is no longer a problem.
  
  NPR interview with an NTSB guy I heard a few years back with a bit of googling around (again, years ago). Hence the "IIRC." Snopes has details on why phones themselves aren't dangerous around pumps.
  And it's still a problem - it's just that it's not the phones themselves that cause it. You'll notice that pumps now tell you to stay by the handle and not get back into your car.
  
  In the UK you have to stand there and hold the pump. They don't fit the catch that allows the pump to keep going while you don't hold it. The pumps in the US are very convenient but petrol streaming out potentially while no-one is paying attention always feels like a bad idea.
  
  I've had fuel pour out once - but not from the pump. We had someone replace the fuel pump and they forgot to put the gasket on.
  I agree it sounds like a crazy idea, but it works. The automatic cutoff on those fuel dispensers works really, really well. I've been driving for over 30 years and have never seen it fail.
  
  I'm not sure exactly how it's done (I'm guessing some sort of pressure or seal mechanism), but the pumps are also designed so that if the pump isn't fit properly into the car's gas tank, the catch will automatically drop and the fuel will stop streaming. So if you start to pull the handle out of the tank while it's still pumping fuel, it'll automatically turn off
  
  Mythbusters had an episode about it
It's probably just a precaution measurement or for liability reasons (like don't put your hamster in the microwave).
Here's more to read: https://www.snopes.com/fact-check/fuelish-pleasures/ The rumour of cellphones not to be allowed at gas stations has proven to be false.
- People used to be paranoid about it. I was using my cell phone at a gas station once (15+ years ago) and the cashier remotely shut off the pump until I put my phone back in the car.
- I mean, I've personally seen a sign on a gas station that tells you to leave your phone in your car, so no.
  
  We do have these signs (crossed cellphone) also at gas pumps where I live (Germany). As I stated above, I think these signs were introduced with the beginning popularity of cellphones and serve mostly as a precaution measurement because nobody knew 25 years ago if cellphones pose a harm to gas pumps when both are in use simultaneusly. In the same fashion that cellphones had to be shut off during the entire flight in an airplane. Gas pumps were there before cellphones. I personally witnessed people pumping gas and use cellphones at the same time and nobody cared. Depending on where you are from, your experience may differ.
  Edit: typo, spelling
  
  Signs don't mean danger
  
  The rumour of cellphones not to be allowed at gas stations has proven to be false.
  I was replying to this. The comment doesn't claim it's not dangerous, it claims it's not forbidden to use them on gas pumps.

And here I'm paying for gas using phone near distributor. Well it can be dangerous when someone try to stop you because they think you didn't pay for gas.