The whole point of a casual, social guild is that you don't NEED the guild, you prefer it for the social aspect. Hardmodes are actually a very small percentage of the achievement points you can get. Think of all the fun you could have getting the holiday meta achievements with a group of people that you have fun playing with, without the pressure of getting it done before raid time. Or instead of spamming guild chat with questions about which bracers you should be wearing, asking about that cute new vanity pet that you saw in Dalaran.

Wrath created a different class of casual. Just as they opened up raiding to casual players, they created a whole slew of achievements to point out the casual gameplay themes that already existed while also adding more casual play elements that are well "below" the raiding curve.

The whole reason my GF won't join a guild right now is because of the elitist attitude that any achievement worth having requires 25 people working together flawlessly and the pressure that can come with that. She likes farming for vanity pets and mounts. If you put her in a group of people clearing Strat repeatedly for the Baron mount, and let her squeal in fear at the spiders to her hearts content, and said, "Hey, just spam Rain of Fire on my head," She'd love it. No one critiquing her gear or her build. No one needing her to be online at a certain time (because they are easy and they don't NEED her to be there at the top of her game).

The obvious slack-jawed answer to this is to tell her to go play Hello-Kitty or Pokemon crap. But she likes WoW. And WoW has many elements that cater specifically to her playstyle. She can't be alone in this. Why not have a guild for it?