I'm relatively new to Showdown, though I have been playing by Smogon rules since the end of Gen 4. I've been around from the very beginning of Pokemon games. While I am in no way an authority on Pokemon, or anything more than a slightly competitive casual player, I felt like putting in my two cents in on this thread about Aegislash.
I hate using Aegislash, because I'm the type who likes to try to win outside of the typical norm. Unconventionality is just how I am, and I understand what that means going into OU where there are a very specific number of pokemon considered viable. I know Aegislash is a very dangerous foe to take on, no matter the set its running. Novices who use the pokemon can still make it effective just because of Kings Shield alone. In a metagame thats full of predictions and counters, which I personally feel is about skill, Kings Shield always felt more gimmicky in the sense that it requires little to no skill. Yes, like any pokemon, its always going to be much more dangerous in the hands of someone with more skill and experience, but the fact that having no skill to be able to use Aegi is just frustrating. Many arguments above mine point to Versatility, 50/50's, and that it has very unreliable checks and counters to it. Neither of these things alone would normally mean much, but toss all of that in with Kings Shield and Stance Change, and its nasty to deal with. Since I have am relatively new to playing on Showdown, I haven't often seen it in the hands of a competent player. I can usually sack off something and go into Clefable, set up a Calm Mind and blast it with Flamethrower, dangerous I know, but it can work.
Unfortunately though, Aegi can destroy my whole team with relative ease, even in the hands of an incompetent player. A pokemon like that takes little to no skill to use, when any kid can google how to make a clean set and play it on Showdown or x/y, and this is mainly due to it not having many legitimate counters. I always thought pokemon that took no skill belonged in Ubers, and I still feel that way. With great typing, perfect sets to run, Kings Shield, who wouldn't want to spam one in there party when it can bring so many wins with relative ease? If I didn't have the weird pride that I do, Im sure I would be running one as well.
Versatility in Pokemon is great, but not when its just one team limiting the top of the game where running it is the only way to be at the top. I don't want a metagame where you build your team with one super pokemon, and the rest of your pokemon are used to counter the same pokemon on the other team. What is the fun in that?
I vote ban on this obnoxious, pokemon that limits OU due to its use.
As for some of the arguments above that I have seen, I have a few comments.
The one that annoys me most is the "If we ban Aegislash, another pokemon will just takes its place."
Sure, you could argue that slippery-slope style argument, but Aegislash has one thing that it uses like no other pokemon, Kings Shield. While another may rise to the top, KS wont be on it. Lets be real, Smeargle can learn it, but without the stats of Aegi and Stance Change, it will never be the same. And like another argument defending this pokemon from being banned says "We shouldn't ban this pokemon just because it doesn't have any reliable checks or counters", then the opposite could be argued. Any pokemon that is currently in uber, like Blaziken who doesn't seem to have many reliable checks and counters, could be brought back to OU by that logic.
If I see any more annoying arguments, Ill add em in somewhere.
~Titania