Einstein one said that things should be "as simple as possible, but no simpler". "Madman" Muntz, who I can't explain but only point to his wikipedia page, would walk around the labs of his company with a pair of diagonal cutters and would snip parts out of his designer's circuit until it finally stopped working... at which point he'd tell the designer to put the last part back in and ship it that way.
Bikes are kind of like that. You can buy a bike with all sorts of neat features. Dual suspension. Racks. Lights. Massive gearing. Tires that will roll over anything. And, you know, all that complex stuff does get in your way. If you have derailleur gears and indexed shifters, they need adjustments. Racks are dead weight if you don't need them. Even the ratchet in a freewheel is something that needs regular servicing and replacement... and if it's cold enough, the lubricant inside of it will seize up. Sometimes it's just better to get a track bike, which is pretty much as simple as you can get before it stops being a bike.
But it turns out that the more complex bike with gears and the ability to coast will often let you go places that a track bike without gears won't. And, while you can carry some load over your shoulders in a backpack or messenger bag, eventually it's easier to bolt front and rear racks to your bike and use panniers, which track bikes don't tend to have the eyelets for. So, while there's this beautiful zen simplicity to riding a track bike, it's only as simple as possible for a defined region, beyond which it's too simple.
I have nothing against fixed gear or single-speed bikes. Honestly, I'm the sort of person where, once you removed the restrictions of money (I'm a stingy twit) and storage space (I live in a Silicon Valley apartment) I would have one example of each type of bike. The track cyclists who kept the fixed-gear setup alive know damn well what they are doing. If you are going to set the hour record, the few minutes you have to stand on the pedals to get yourself going aren't important, so you can totally just use the final gearing you need on a fixed gear bike. And the bike messengers who pedal around cities who rode fixes set up with aerospoke wheels, short handlebars, messenger bags, and so on knew what they were doing. For both of these cases, they are riding a bike that is as simple as possible, but no simpler.
On the other hand, it is very easy to put a fixed gear bike into a situation where it is too simple. If the name of the game is to get yourself across hilly terrain without needing to find a mountain pass (that might take you an extra hundred miles than the direct route) or without blowing out your knees, maybe you should get gears.
The difference between a bike messenger riding the aforementioned fixie with aerospoke wheels, short handlebars, and no brakes and who is wearing a chain around his waist and a u-lock in his back pocket and a messenger bag and a similarly clad hipster is that the bike messenger has carefully optimized his bike to suit his problem, whereas the hipster is blindly copying somebody else's optimized solution without consideration for how well it solves their problems. And, from there, riders will try and further optimize the configuration like seeing who can have the shortest handlebars or realizing that they can't skid-stop very well and adding brake levers to weird locations instead of in the handlebars... are doing so without any understanding of what they are trying to accomplish.
Personally, given how much more fun riding is when you can bike up a mountain without screwing up your knees without being a very high level of cyclist, I like having gears.