I'll offer a contrary opinion.
1) For most of the reasons people mention for the use of QD mounts one can do the exact same thing with bolt on mounts--just use a wrench. If you're going to the range and plan to swap scopes around...why wouldn't you bring a torque wrench? For cleaning and storage at home...do they not have a wrench at their houses either? And for some mounts which can be removed with a small L wrench kept in a compartment of your rifle's stock (yes, wink, wink) in the case of a broken scope you can remove it to use your BUIS in a few seconds no matter where you are, even if all you have with you is your rifle. So unless the charging zombies are only 20 yds away and closing fast, it's just not an issue for most people.
2) My experience has shown most of those who think they are suffering no downsides really are but simply don't know it. With an accurate enough rifle and methodical enough testing, it can usually be shown. The biggest problem is most typical QD mounts set up the way most people set them up only put around 1/10th the clamping force on the rail a good bolt on mount will. This is why the first shot of a group after reinstalling the mount is often a flier, especially with rifles of more recoil than the 5.56. The scope actually moves a significant amount under the recoil of the first shot.
But if you push it all the way forward while mounting this isn't an issue, right? Well sure, just be careful not to accidentally thump the butt of the rifle on the ground (easily generating more g-forces than the recoil of most AR's--only the other direction), shifting the scope backward again. So, if the rifle gets handled a bit more roughly than your typical range-queen it's something to think about. How about big magnums with a brake generating negative g's with every shot? Some of my customers with Barretts and DTA's were having fits trying to get them to shoot until getting rid of their QD mounts.
Don't get me wrong, I know there are applications where a QD mount is a better choice. Swapping with NV gear as some brought up above, or if there really is a good chance somebody will be shooting at you when you break your scope so every second counts, sure. And for the vast majority of AR owners, especially 5.56's, with a 1.5 MOA rifle that's never used beyond 300 yds, frankly they're never going to notice the difference.
Anyway, there' some more things to think about when making the choice.