"You don't need X if you're not retarded."
"Why make this ridiculously easy game any easier?"
These are the kind of statements you see from Self-Gimping Elitists, hereafter known as SGEs.
What motivates them?
Perhaps they are just trolls. Maybe they have fragile egos and need anything, just anything at all, to maintain their fragile sense of superiority. Or, are they just that good? Are these gods among men?
I suspect it's one of two events.
1) Direct attack: They didn't have an expected tool and were attacked for it, so they respond by claiming that X tool isn't needed. Maybe it's Omen and a claim that you can just get a feel for your aggro.
2) Perceived attack: Change can be scary for some people. Sometimes there are legitimate concerns with new tools replacing personal ability. I'll try to say more on this later. New things are rejected purely for being new.
What is to be done with a SGE? Treat them as you would any other player. If they aren't showing up with the required addons (required by the leadership, not necessarily needed by the game itself), kick them until they get them. Do not coddle them. If they want to argue about it, fine, just as long as they do what they are supposed to. There's no sense in frustrating everyone with that one tank that won't use Omen, so no one can tell where they are.
Do they have a point? Well sure, almost every addon isn't needed. I bet raids could be done with no aggro meter. You're just going to lose a lot of DPS as people either go too far and die or hold back and end up far below what they could do (this is in fantasy land where tank aggro isn't insanely buffed, I realize that now you could do a lot of content with full DPS and no aggro meters). Buffing can be done without PallyPower. Call out assignments, have paladins watch durations themselves, watch for deaths to know when to rebuff. It's not impossible and doesn't really require any skill.
But, why? What is gained by refusing to use tools? Why spend any extra mental effort to watch deaths and individual durations when an addon can do that for you? Pay attention to the pulls, health bars, debuffs, pats... Frankly it's stupid to use any more than the bare minimum amount of effort on tasks like buffing.
The argument about losing skills is certainly a good one. Basic knowledge gives a larger mental tool set. I suspect that if people do not understand addition or multiplication (aha, they are really the same thing!) or decimals, they cannot understand the world. We live in a world of numbers and if you cannot understand the basics of how they interact, you're lost.
But let's relate this back to WoW. A guild I ran with for a few weeks kept letting me die on Gruul. Notice that I said letting me die. I wasn't undergeared, taking excessive damage, standing in falling rocks, or hugging people during shatter: I just was not getting healed. The problem was Healbot, or more accurately, how their healers were using it. They depended on it completely and may not have been using it properly. As a result, I received no heals. I told them to turn it off and they freaked out because they were too worried about overhealing, wasting mana, and then going OOM. A few former guildies of mine (we ended up in this guild after a merger, so they were still in my guild, but I thought of things in terms of my previous guild, which we were obviously no longer in) went along with my advice and just started ignoring healbot. They used old-fashioned timing, proactive healing, canceling, and yes, a good bit of overhealing. After that I survived just fine.
Don't be a SGE: Use tools. They're useful; they minimize the tedious aspects of the game. Don't depend on them.