The error here is to conflate need with an involuntary act. You have probably found that as you get older you need to anticipate when your shits come as often as you voluntary take them. That’s why the elderly wear diapers just like babies. At bottom you are therefore speaking about an involuntary (or semi-voluntary) act and trying to make ethical hay out it. If this were correct then @Hanover’s dog would be a moral philosopher.