How could one possibly believe that this wall of rambling text would be easy to read?
I think some posts are going in to the right direction, i can understand people who do not want others to suck and wipe their raids, and i can also understand those who want to help other/weaker players to improve.
Frist of all it is important that you should not kick someone out of a raid or guild who has a bad day and sucked for some tries. you should kick him if he really does not want to improve and keeps failing on the same fault every single try although you told him how to do better. I look at my self as a very focused and good computer player, I always wanted to be a "good" player in the games I put some effort in. But we all have a bad day, even a week or a month, on which we can clearly suck. That can be personal problems, like family, girl/boyfriend, problems with the job or with studying or just because it is raining outside.
We all have those phases, and I think nobody can say that he is always(!!) able to give 110%.
In my old guild we had some problems with a paladin, she always died first, progress and farm, she did the worst healing was always inferior to all other healing classes, and sometimes even behind shadow priests. You know the gimmicks all chars do if you don't do any action? Like she plays Bloodelf and the model of her char always moved the head and looked to the side, so you could tell that she wasn't doing anything at all. It really frustrated me since i could not understand how anyone could play with that small focus to the game. I often told my guildmaster to kick her or at least don't take her with us to progress stages but he always refused since he did not want to have a bad clima within the guild (her boyfriend was a officer and thought she would be doing a great job).
After I left the guild I still was chatting with my old mates and was always hearing that she did not improve. So what would you do? In my opinion it does matter in which positon your guild is, like hardcore casual, or something in between that. But I also think that you can not always help people to improve in playing a game in which the original goal was to have fun. Of course some people like to help others improve, some are doing this just for fun, but I think you have to draw the line on some point. When people really try to improve, try to get better stats on dps or hps that is always good. But if the person just can not do it and still sucks you can not take her by the hand and let this person suck the energy out of other guild members. And when your guild is trying to get "harcore" people just can't suck over a couple of month. Even weeks are just too much time.
I remember our first visits to void reaver in TK. The mentioned paladin did manage it to pull void reaver ~ 3 times, without beeing told to do so. After those 3 times she was so carefull that she did not manage to heal the tank for over 10-15 seconds, which also resulted in some deaths. Anyway we did manage to kill the reaver but the paladin managed to cost us up to 2 hours to do so (respawn inc. etc.). Some ID's later she still pulled Void Reaver one or two times, and I can say that really sucked my energy out of raiding with her. I always tried to get off raid days where she would be in the roster and so on.
What I want to say is that you can not always wait for people to improve because it can turn out that bad, that the good players will leave because they do not want to waste their time on this. If you are farming content you can do improvements with players that suck but in progress time everyone should be able to do his or her best. And if someone knows that he has a bad day he should say "i am out for tonight, get some substitute for me" (if that is possible, on a maintank position you'll have a problem :>). Everyone wants to raid but if I will constantly wipe the raid due to some personal circumstances I really should know that giving up the slot is a much better thing than just doing your "job" and suck.
Some people just can play "good" and some can't. In the German Community it's always said you do not need "skill" to play wow, it's just pressing some keys. But in fact, like in any other game, or sport, or whatever, you do need an amount of "skill" to perform on difficult encounter. And that is nothing personal. I can do shit in math, I always use a calculator for the easiest tasks and i really am not happy about that. But it's a flaw I can't work around or get better in. So I will never be a math teacher or scientist or what so ever, that is a fact. That's nothing against my person, or my intellect it's just a fact. And some people can take the fact that they officially suck in wow. They always think you want to insult them, or get them out of your way. But in some times it is just the fact that they suck. They can do a good job at karazhan, gruul, even in SSC. But when it comes to the point where they have to do a really good job, they will fail.
Some people don't want this to be true, but it is