Now I'm interested in what your answer to the why not question would be

I agree with the other posters every one's in a different situation some may want to be working others not, some may be happy with their childcare arrangments others not etc.
I don't think you need to be afraid of having a conversation about this unless you feel the need to take a 'childcare is bad, it will harm your children, no matter what the situation is/was childcare is the wrong choice' type of stance. Even if you don't think childcare is bad as long as you don't have a problem with others using it and allow them the space to make their own decisions and not have to feel guilty about them, then I think it's absolutely fine. So basically as long as you explain why you're not using it for your situation and don't just start telling anyone who is using childcare that they shouldn't because it will harm their babies, I wouldn't expect it to cause confrontation.