Beesknees, I am not saying whether I think this is right or wrong - I mostly tend to think people have to do what works for their own families.
However to answer your question, what children grow up with tends to be what they view as "normal", and there is a lot of sexism that we accept as the "norm." Things such as Dad driving the car, for example, and it was the same for me growing up. We used to sometimes drive to Wales on holiday and my dad worked in Warrington in those days so Mum would drive me and my sister to dad's workplace then they'd swap and Dad would drive. Why? 
Dunno, but that sort of shit gets ingrained.
Now, while there are SAHDs and I'm sure half of Mumsnet will now descend on me to say their partner is a SAHD, the majority of non-working parents are women, they are SAHMs or they work part time, which means they inevitably take on the lion's share of the housework, childcare and things like school pickups and attending school plays and so on. So for young children, the idea is that we are defining gender roles. Dad goes out to work, Mum stays at home. That can be damaging. Parenting is two roles: caring and providing. It shouldn't fall entirely on one parent to do one role. It should be a combined effort.
Now there are households where people say and it's a fair enough point, one parent earns so much and all "she" could get is a minimum wage job and why put the family through that stress? Well, yeah. Problem is, and funnily enough I've just been having this conversation with my Year 10s, who are studying An Inspector Calls and we are talking about Gerald's relationship with Eva/Daisy, if you know the play. I don't personally think a relationship that is so unequal to have one partner able to earn considerable amounts and one only minimum wage is healthy. If that was me, I don't know really. Just that presumably if you can only get minimum wage and so perhaps levels of education aren't great and blah blah ... I am probably wandering too far into idle speculation but as far as possible relationships should be a meeting of two equals, not one where one is significantly financially inferior.
Moving onto the next point, I don't think it's a depressing notion but a pragmatic and sensible one. It's by no means a unique situation that a woman gives up work on having her first child, there may be a vague plan to go back to work when youngest is at school but by that time comes round it's been ten years out of work and things have moved on and anyway everyone is used to her being at home and she has a life based around that expectation and friends and a social circle and before you know it two and a half decades have gone by, the kids are 25, 22 and 20, and she's in her middle fifties and he fucks off with plans to sell the house, yes she gets half but it isn't enough to buy another place outright, so once that lump sum (which she wanted to spend on her children's weddings, house deposits and the like) is spent, she's forced to work for minimum wage and live a life of poverty.
Poverty is shit no matter whenever or wherever but honestly, doing a minimum wage type retail/care/cleaning job in your mid fifties is perhaps the shittest after a life of relative comfort and free of stress. The real shitter is that if you grit your teeth and stay in work, you can actually wind down at this point.