At the beginning a family is made of two parents. When only one parent takes such dramatic decisions as to lie to their spouse in order to hide its cheating under the umbrella "its for the best of the family", then I stand to my point of view: this person is acting badly (shortcuted to "a bad person").
And I can understand specific contextes, so don't come up with things like "what if the other is handicapped".
But it's ok, you place value in peace of mind, I place value in respect, different points of view, nothing new, no big deal.