Smogon is a website that created a tier list that people can choose to follow. Some people follow it to a T and will not play anything outside of Smogon's ruleset. Some people vehemently oppose it and wish it never existed.
There is no reason for it to receive such heated debate. It is a website with a ruleset and tier list that you can choose to follow if you like the way it is balanced. It has some positive factors and some negative factors. If you don't want to follow it, you don't have to. If you want to follow it, you can.
I don't play Smogon's metagame, and couldn't care less about it really. Won't ever see me initiate a random battle using Smogon rules, of course I'm open to accepting battles using them. The users do put in the work to research every mon competitive slowly but surely, and furthermore Smogon itself doesn't hurt anybody. No one is forced to play under their rules, rules that are considered optional by the default set. Sure you can find unpleasant individuals from Smogon, but the same could be said about any forum(cough). Smogon's not some sort of Golden Standard, but it is a standard that works for a lot of people. Which is ultimately not a bad thing.
Nobody made Smogon "king", that's why their rules are considered unofficial. You say we should do what we want, and that's exactly what competitive battlers are doing when they follow Smogon. The people over there do their research, and the rules and tiers they come up with are much better than anything the average individual can come up with.
If you try to battle someone without any kind of standards set up, you're most likely going to run into several of these problems:
*Spore spammers sending your entire team to sleep because there's no sleep clause.
*Evasive move abusers (last time I checked, moves like Double Team were banned, and for good reason)
*Legendary teams consisting of Pokemon like Arceus, Mewtwo, Rayquaza, etc. that completely overpower your team consisting of average Pokemon.
*Wobufett. Damn, I hated these things before they were banned... They're still banned, right?
Sure, you could negotiate with someone before you battle, but chances are you'll just simply come up with rules similar or inferior to Smogon's rules. Plus, it'll take you longer just to negotiate towards what Smogon already has. It's most efficient to have everyone unite under the same community rather than have everyone do their own thing. Nobody's forcing you to follow Smogon's rules, but like someone else said, don't be surprised if nobody wants to battle you.