I think it depends on how old the DC(s) are.
Plenty of parents (normally but not always the female parent) decide that they want to be a SAHM when the DCs are young (it's not always forced upon them due to the other persons' career but i appreciate this can happen).. but once the DCs are at school then many couples find a way to make both parents having a career / job , even if one partner travels a lot.
No in some cases it's not ideal and it can get a bit messy along the way but there is pretty much always a way round these things.
I needed to find solutions as a single parent once the DCs started school pretty much every school year as I worked full time and things always worked out.
Plus why would you willingly become reliant on one person's salary and miss out on years of NI contributions unless there really is no other option?
Of course if you have DCs with SEN needs (as I do too) then things need to be thought about more carefully but if things are straightforward then I think it's a vulnerable position for anyone to put themselves in.
However I don't agree that benefits which are being paid for by people who have nothing to do with the couples' family should be responsible if there is enough money to go around for a period of time. Not forever but giving the person who has not worked a chance to get themselves to a position where they can support themselves better.
The reality is (as I have experienced first hand as have many others ) that both parties are normally worse off when they have a family and they separate. That's what happens in most cases as 2 households have to be supported. Not all but most. That's just logic, maths, life. It's not easy and it's a bit shit sometimes but there's is always a risk when you have a family or get married.