Originally Posted by Akka

I beg to differ.
What I think is incompatible, is having a mix of "casual" (for what the word is worth) and "hardcore" in a guilde with hardcore ambitions. In this case, skilled people with lost of investment will feel held back by the less competent players, which will lead to tensions, and the "casuals" will probably resent both these tensions and the fact they are pushed hard to play more/better.

But I find it's possible (though, of course, it has its own problems) to mix both kind of players if you announce from the go that your guild likes progression, but will stay somehow casual, and that you keep your ambitions somehow low.
Such guilds are more interested by social interactions and friendship/ambiance. And there is no game skill needed for these, so they can accomodate both hardcore and casuals - unless, of course, you consider that a "hardcore" player is a player whose main ambition is progress, and not just time played/skill/involvement.