ie . recognising that it's accrued family wealth that determines financial independence and it's not necessarily always as simple as who earns what. A SAHM may well have greater financial independence than a woman on a high salary, depending on that family's underlying financial circumstances
A sahm with no income is completely dependant on her oh's goodwill to hand money over. That's just fact.
If the oh suddenly said, two days before payday 'right I'm off, met a new bird, see ya' then the other partner with dc and no shopping in is fucked. If rent is due in two days, you're fucked. You apply for UC or whatever, have to wait for the first payment, struggle through... then you're in the far more difficult situation of trying to find a job after x years out of the workplace. Your pension is lower as you've not been contributing.
If DH fucked off tomorrow I'd be in an awkward position, sure. Our lives are built around two incomes, there's no denying that - I'd have to make some serious adjustments sharpish.
But I have my salary coming in. I'd apply for UC as a top up/help with childcare and hopefully get a small amount extra, but I would have enough money to stay in our house and cover the bills and food (just!) without any immediate panic.
It's not just about financial vulnerability either. It's about economic vulnerability. I have 3 dc, have always worked. I've gone part time when each dc was small then bumped hours back up (in the same job) when they go FT...and I pay far more from the family pot into my pension than DH to make up for these 3 hits of maternity/part time. DH knows that and fully agrees - if he didn't, that would be a red flag. My CV is up to date and I'd be in a good position to look for a better pair role in my sector should the need arise. Much harder to do with a gap of x years behind you.
I don't 'sneer' at SAHMs...but unless they have an established career that's easy to step back into and independent wealth or savings, I do think they're crazy.