I can totally agree with that. I can't say i was ever in a casual raid guild but they were always fairly relax on what amount of days per a week people raided. When burning crusade came out, my guild kind of made a switch to being more "hardcore" and many people started to be left out since they pretty much went with the same group every night with no flexibility for the other people in the guild, even members that had been in the guild since the guild was created way back when WoW was still in beta.

Long story short, many people quit the game because they had just come to a point were they couldn't do anything more in WoW. Personally, i made a new character on the opposite faction and had fun not only experiencing a new class but also i levelled on a completely different server. I found myself hitting 70 and instantly in a very casual 25 man raiding guild. I could pretty much raid what day suited me best and i wouldn't be left out. The trade off was, the progress was a lot slower than my previous guild but everyone was really nice and sometimes you have to make a sacrifice. If you want a guild thats more casual, you might just have to accept its going to have slower progression. Of course it still needs to have some progression, other wise its the right thing to look for another guild.