You're half-right. According to Nimzowitsch, doubled pawns are a static strength and a dynamic weakness. If they don't move, they're hard to attack. But when you're trying to advance doubled pawns, they get in each others' way. For example, in the Ruy Lopez exchange variation (played by Fischer, Lasker, etc), white voluntarily doubles black's c-pawns in exchange for the kingside majority, with the theory that black's queenside majority will be harder to mobilize in the endgame.