I don't think it's bad not to, no. There's plenty of other ways to get the same thing.
My DS is in daycare 2 days a week - intitally it was because I was working, then to have a break, and now simply because he enjoys it (I don't get a break now since DD came along).
I find it interesting when people fret about 'socialising' their kids, when really all they need to do is interact with them.