From my experience I feel that a lot of this stems from turning midwifery into a profession that is perceived to be almost on a par with medicine. Midwives are not medics, they do not have the same academic and training background, yet they are making life and death decisions about women and babies.
I still find it astounding that you can have a midwife led maternity unit miles from a consultant lead unit, so if things go wrong you have to pray that you'll be ok by the time you are blue lighted to the nearest unit - and how traumatic that must be in the throes of labour. There is very little that midwives can do in terms of intervention.
During my first pregnancy I was pushed into using the local midwifery unit and naively thought this would be ok and couldn't understand why mother was freaking out a bit about this. As it turns out I ended up at the consultant unit due to high blood pressure and thank god I did as I ended up having an emergency CS. Which is another story.
But I will never forget going to the MW led unit one night near to the birth as I had a small bleed and feeling extremely anxious and vulnerable. The very young MW lectured me(in front of my DH) about how men had medicalised childbirth and how going to the large hospital to give birth was a bad idea as the presence of doctors would result in a very traumatic labour. I just sat there, but if I had my time again !!
But my point is that in essentially replacing doctors with midwives, it seems that MW have a massive chip on their shoulders about intervention and that childbirth is the most natural thing in the world. It is, but it is highly risky for mother and child which is why in the past when we didn't have any intervention so many died in labour and continue to do so in the developing world where people do not have access to proper healthcare.
Which is why I think MW push drug free natural labour to justify their position and existence. I would think that in most other developed nations doctors are responsible for and manage labour from the very beginning.