I never understand the argument that many professions work long hours and overtime, so nurses should - are you bonkers ?? You want someone who is already 13 hours into a shift and exhausted, to stay and look after you when you are seriously ill?!
To be clear, I absolutely DON'T think that a nurse who has already done 12 hours should stay on longer, definitely not. I think shifts should be 8 or 10 hours long, max.
However, nurses I know prefer the 12 hour shifts because they can work their hours in 3 days. The downside of that is if management is poor and shifts aren't adequately covered then it leaves people getting into dangerously long shifts where they are likely to make a mistake. I don't think that should be allowed. I think the shifts should be 8-10 hours, and 4 or 5 days.
Just because you haven't experienced it doesn't mean it doesn't happen. I know a few nurses. The one I mentioned (who could sleep on night shifts) has also worked in busy wards so has seen both extremes, but most places she's worked have been somewhere in the middle. Another is in ICU in a trauma centre where nights are sometimes quiet, sometimes sheer hell. Nurse 2 frequently says on her way out after her shift she she's A&E nurses in tears because they are so exhausted and short staffed. 
I've also had relatives on wards where overnight (and during the day, but it's especially annoying at night) the nurses are sitting chatting at their station and leaving drip machines to beep loudly for 45 minutes at 3am, torturing all the ill people in that ward who need rest to recover. And this happened every. single. night. They weren't busy, well, busy chatting.
Not all nursing jobs are the same. The NHS is very poorly managed.