If the alternative is to break up a family so the cheater can be 'honest' with him-/herself, is a lie and a happy family worse than a broken family? Stop seeing things black and white.
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.
- If someone wants to believe the lies, then in order to avoid discovering the truth, they will keep the relationship intentionally superficial.
- If someone doesn't want to believe the lies, they will discover the truth sooner or later and they will just be acting through life.