I confess I haven't RTFT, but there are so many reasons for deciding to be a SAHM.
For DC 1, I was tied into a contract which allowed me 10 weeks mat leave if I wanted to return to my original role. None of it was paid (hello Channel Islands, back in the day!) and we used up all our savings to pay the bills during that 10 weeks. I was the higher earner as well, so it was a huge hit.
Luckily found reaonsable child care, but going back to work, as a full-time breastfeeding mother, wasn't easy AT ALL. Luckily, DC took expressed milk from a bottle, but God knows what I'd have done if they hadn't. But that's by-the-by.
In terms of finances, things were joint all the way through. And that's the important thing for SAHMs, no matter where they are, or what era they did it in. Without being joint, I'd have been sunk. At no point was I expected to 'fund' all the childcare either. Once I returned to work, it was all pooled.
With DC2, though, I was in a different role, and we made a joint decision that I would be a full-time SAHM until DC2 went to nursery. And when they did, I only went back part-time. By then, DP was in a better-paying job, so we could take the hit, but for quite a while things were tough financially - I was given an amount in cash each week (which I fully agreed with - I knew what our finances were like) and we lived within those means. It wasn't easy. But it was worth it when we looked at the bigger picture.
Now DC are several years older, so it's not so bad. But I have no regrets because I know we were on the same page from the start.
I think MN posters (rightly) have an issue with SAHMs who are forced (even if 'nicely'...) to give up their access to joint money and equal access to decisions to what is done with it. That's where it goes wrong, and where the (for some) prejudice comes from against SAHMs.
It's a mine field, there's no doubt about that.