I guess it is up to people whether they want to work or not.
All I would say is: unless one is independently very wealthy (i.e., trust fund baby etc.), any decision to withdraw from the workforce should be predicated on the following:
1: The relationship with the breadwinning partner should be legally recognized (marriage, civil partnership or multiple contracts signed up with a lawyer).
- Wills, insurance etc. need to be in place.
- The SAHP MUST have a good answer to the question "What would happen if it all went wrong and you had to support the family?"
Some people have careers that they can easily dip back into--good for them.
Others have careers where a long break will make it hard to go back in: in that case, better to keep one's hand in in some way, like relevant volunteer work, networking and other activities to maintain connections and keep your skills sharp. Or ditch full-on SAH and choose to work part-time--even if you make nothing after tax&childcare, you can look at it as a form of insurance and will probably enjoy the challenge, and having some time away from the kids.
Some people ended up SAH because they became disillusioned with their careers, in which case it is a good idea to use the SAH period to do some research into what you would like to do, and do some reskilling or retraining.
If people do the above, fine.
What I DON'T think is a very good idea is to drift into SAH without any clear idea what what one is doing other than a vague idea that "a man is a plan." It isn't. You need to think about worst case scenarios--marriage breakdown, accidents or illnesses leading to early death or disability, the possibility that the breadwinner might start to become resentful of the SAH partner, no matter how supportive they may have been at the beginning when the kids seemed so small and needy. There MUST be a Plan B for what happens if the situation changes and SAH suddenly isn't possible or desirable any more.
And the situation is frighteningly perilous if a woman (it is usually a woman) has been foolish enough to become the stay at home "wife" to a man who will not marry her. If he runs off with his chiropractor or gets hit by a truck, she could be left well and truly up shit creek. If many years have passed, she may have difficulty accessing anything other than the most menial jobs. She may have no stake in the property or savings, depending on finances were arranged in her relationship, and she will have very little automatic claim because "common law" spouses are not a thing in the UK. She is unlikely to get spousal maintenance and any child maintenance will stop when her children get to 19 (I think). She may be left with nothing but a pitiful state pension when she gets too old to do whatever work she manages to get hired for.
Bottom line: if you are going to SAH, do your research and be very aware of possible pitfalls.