We don’t say people make monastic vows are somehow doing something inferior by ruling out marriage. If a civil partnership is made together with a public vow of celibacy, then the closest analogy is with religious communities. There may be a place for affirming (even blessing) such a relationship. But the key point IS the public affirmation of life-long celibacy even if it were possible to be sexually active. Without that the relationship is open to being sexual.