Equality between partners is healthy — couples have stronger emotional bonds and feel like true companions. There’s mutual respect, so they have more effective ways of communicating, and are more open and supportive of each other.
A relationship that’s one-sided isn’t satisfying. Certainly not for the submissive partner, who may feel they have no control over their marriage, and sometimes over their own lives. Those playing that role are likely to lose interest in their relationship because their needs are regarded as secondary, and so often unmet. Furthermore, because they’re treated like a second-class citizen, submissive partners may feel angry and resentful, and certainly not emotionally connected.