Some subjects attract nerds and geeks like a candy atracts ants. Computers. Trains. Planes. Model trains/planes/cars/boats. Photography. Personally, I was only spared from the aviation mania.
Like so many hobbies, photography is attractive because it combines art and technique, advanced science with empiric method. Nowadays, photography and computers go hand in hand like never before; almost every camera in use is digital, and almost every mobile phone is also a camera.
Negating all prognostics, cameras sell like never before. The hobby is practitioned by billions, even people that only have a cell phone are proud of posting on Instagram.
Affictionados always dread new technologies, as they could kill photography as we know it. Camera phones would wipe out the camera industry. Digital photography did not have the glamour of film. SLRs (*) with automatic exposure would dry the pro market. Before it, autofocus SLR were the devil... I guess every novelty like integrated photometer, Polaroids, zoom lenses, 35mm film instead of large format, SLRs in place of view cameras (that ones with bellows) was dreaded by many as the end of "proper" photography.
Another "murderer" dreaded for a century is the movie, either analog or digital. Who would take pictures if he/she can record a movie? But nobody killed nobody, nowadays every camera is capable of recording movies, and moviemakers are even preferring DSLRs (**) to make entire movies!
Photography is a multi-disciplinary science. It involves physics, optics, math. Every picture involves many interconnected decisions: aperture, shutter, ISO sensitivity, focus, zoom, flash and color temperature.
One level above, every lens and every camera model is the result of a huge set of difficult engineering trade-offs. Not taking disposable crap into account, there are no "better" or "worse" camera. There is a camera that is most adequate to a given use case. The camera inside a cell phone is indeed limited but it is a miracle of engineering, given the constraints. These factors lend a unique "character" or "soul" to every equipment, as if it were a living being.
Nerds love a "religious war". Linux vs. Windows. Star Wars vs. Star Trek. (The rest of the people do Democrats x Republicans.) The strong character possessed by every equipment and manufacturer, gives a lot of motives for endless discussion, exactly what we nerds like most :)
In the 1980s, it was Kodak vs. Fuji films; negative versus slide. Nowadays it is Canon x Nikon, DSLR x mirrorless (*3), RAW vs. JPEG. And of course, Ken Rockwell the genius versus Ken Rockwell the idiot. In another league, some crazy folks are still using film, cross-processing it and looking down on us.
Even though photography is an art. All the engineering around it exists to make the art viable and easier to do. Many photographers condemn the nerd attitude, because discussing technical differences instead of going out and take pictures is losing sight of the goal.
They are not wrong. In the other hand, if some people get their kicks out of these discussions, they are lucky. Some people have fun discussing Canon x Nikon, while others need to engage on binge-drinking to feel alive. Who's smarter?
Different from the measles, the virus of photography can make you sick more than once. In the end of the 1990s, I had a Yashica FX-3 SLR, after having played a while with my father's Zenit. They were 100% manual cameras... not very practical to take photos, while they taught a lot. I should have persevered but sold everything to another "infected" friend.
I got a point-and-shoot camera for candids. It was feature-complete, but never took a picture that was really sharp. It worked, but... This is an interesting characteristic of non-pro cameras: the lens quality (that is the only thing that really matters) is highly variable, and often has no relationship with the price tag. My best film pictures were taken with my father's humble Yashica ME 1.
Then I stayed several years in remission, thanks to a diet of camera phones. It is an illusion to think that a camera phone fulfills all photographic needs, but it is an illusion that is healthy to your finances.
It is curious how a hobby can be simply expensive while another is cheap, sometimes for no reason. Model railroading is cheap. Model planes are expensive. Photography falls between "expensive" and "outrageous expensive". Digital photography did not make the hobby any cheaper, since the money saved in film processing is now spent in a new digital body every three years.
My other hobby is trainspotting. I take a lot of pictures and record a lot of movies about trains. But I had resisted tenaciously to buy a decent camera, because I knew that this rabbit hole has no bottom. Until my wife got fed up and "forced" a solution by buying a nice bridge camera for Christmas.
Then everything began again... The bridge camera has already been replaced by a DSLR, plus lens, plus many other accessories. Me, in full relapse mode.
(*) SLR: Single Lens Reflex. Camera with a mirror that allows to view the scene and take the picture thorugh the same lens. Lens is interchangeable. That's what most people call a "professional camera".
(**) DSLR: SLR camera where a digital sensor takes the place of film. Nowadays, almost every SLR sold is of this kind.
(*3) Mirrorless, MILC or EVIL: cameras without the SLR characteristic mirror. Every point-and-shoot camera has no mirror, but this denomination is reserved to cameras with interchangeable lens and bigger sensors.