Fanboyism mostly originates from the fact that most people aren't able to afford more than one console. From there it leads to "brand loyalty" since it's human nature to validate ones own choices and invalidate the choices of others if they conflict.
At least from my gaming experience I've only been able to have one console per generation for the most part. I had a Sega Genesis instead of SNES, then I had a Dreamcast (one if my favorites of all time btw; Sonic Adventure, Soul Calibur, NFL and NBA 2K series). I used to swear up and down that Dreamcast had "much smoother graphics and PSONE had too many jaggies." After that I had an N64 (never had Mario or Zelda but I loved Duke Nukem and the Wrestlemania franchise). Then I had a PS2 which became my next favorite console ever and I hated Xbox because one I couldn't afford one and thus two, I looked for reasons not to want it (screw Microsoft, they're just ripping off Dreamcast etc. the Dreamcast one I still feel is valid as hell). So essentially that Fanboyism bled over into the subsequent generations but it all started because I've always had to pick one and go with it. Yes it has turned into blind hate and love at times but who hasn't had those feelings at times? Also it's just more fun being on the opposite end to create entertainment even though I can be perfectly reasonable and place myself in the middle (I'm a libra after all). I think many others have experienced the same when it comes to video games. Ideally, if it were possible I'd love to have one machine that plays ALL games including handhelds phone and PC games. But Alas, that will never be since "competition is healthy" (lol what a load of shit. When it comes to gaming, creative freedom is healthy).