I think Golden's post above, and Griff's latest reply are both spot-on, as was Lostsoul's post in the officer's forum where we were discussing similar issues.
I do not think the blame lies with any specific person or guild, or that anyone was trying to suggest that. Drawing on Lost's post, we seem to have several categories of people:
1) Veterans who are totally bored of Kara having done it so many times
2) Veterans who may still have an odd upgrade available, or would be after badges, but have done kara so much they want quick and effective blizz through and no wiping or practicing tactics... If these people are placed in a group that has to start learning curator fight from 0 again, they will get very bored or discontent. Fact is that with too many alts/newbies the kara raiding/learning starts from 0 again.
3) Those who still need/want to do kara. This last group is most heterogenous and includes at least: a) Those tribes members who have just started raiding and lack gear and skill/experience,

alts of veteran players
(I hope Lost doesn't mind me nicking some of his words, but they were very well put).
I realise some people may see the attitude of people in categories 1 and 2 above as selfish - but I dont think they are. Many people here have done Kara since >1yr ago, and have done it for 6months+ to help others while needing nothing further there themselves, so I don't think it's really selfish for them to only be inetersted in fast badge-runs, for example, rather than wiping to cuartor with an over-new laden group.
Recent attempts to set up signups for Kara have led to too alt/new-heavy groups in my opinion, which has led to the recent unhappiness.
I don't think any of us has the answers, but I think there are definitely two separate needs to be met; the 'advanced' need of those who have done it forever and should not feel guilty about doing a fast advanced run, and the 'progress' need of people who need to advance their play and kit by progressing through the earlier bosses.
Whatever approach we end up taking I think has to meet both needs, otherwise it gets no-where and leaves half the group unhappy, which no-one wants; but both sides also have be pragmatic about the others needs also.
As.