Midwife here. The actual act of free birth isn't illegal, what is illegal is if anyone attends the birth who is not a registered professional and they could be prosecuted for acting as a midwife without the requisition professional qualifications.
What makes me sad about free birth, is that these women have obviously been either so let down by our services, or are too scared to access them and we (the NHS) are obviously not meeting their needs.
What makes me sad for staff, is that sometimes we are called to attend these births in really sad circumstances, or they have got themselves to hospital much too late and the inevitable has happened.
Often there is a bit of confirmation bias 'well I did it and I was okay' but there will always be one who isn't okay.