Injia there's a huge difference from denying someone content, and not choosing that player for your raid. Whilst you're training the hypothetical "casual" player, the other players in your team are getting irritated carrying their dps or healing, unless they know specifically it's a gearing issue (we for instance currently have myself and a DK who are undergeared because of rerolls but having raided with the guild since it was formed, they know we don't mess around). The best place for these players to learn is in a social guild doing simpler content (which is why I've started supporting ascending difficulty normal). At a progression level you should be the finished article. Let's be honest, that's how this game has always been. Poaching happens, players applying to a better progressed guild happens.
Last raid we had to bring a social healer because our main healer was absent. Our healing leader is amazingly even tempered and even he got frustrated because this guy would not listen and would not pull anything like his gear says he could do. Imagine that on an unknown quantity who is applying to you with one word answers and half ungemmed gear.