As already mentioned in a greeklish / full greek post, I couldn't agree more on that.
It's just common sense that no raid is viable unless all or most members are adequately geared up. "Adequately" for all classes can be easily found in another thread around here and I urge everyone who hasn't checked it out to do so.
As a rule, I would only quickly note here that hit rating / spell hit rating is the MOST essential stat to look after in the pve world... Unless you want to see half your hits miss or get resisted and your dps go ridiculously low. Please check Blizzard's or wowhead's forums on your class - you will find several guides on pve gear and builds as well as answers and advice on any questions you might have.
I really don't bother running normal instances to help ppl gear up and if anyone needs me, I'll gladly join. However, it is everyone's own responsibility to learn how to play and gear his / her char in the most efficient way. In other words, undergeared people should put some effort themselves and not rely only on other people's help (and boost).