Unless you are prohibited from working by the cost of childcare, or prevented from working by a controlling husband, the decision to become a SAHM is like anything else in life, a cost-benefit analysis.
Of course if you have zero assets and would be solely dependent on your husband's salary, I wouldn't recommend living indefinitely like that.
You can't be a SAHM with a man who sees money as anything other than family money. Even if you were earning, it would all be one and the same. You have to have a husband who respects you and who values and appreciates your role (and vice versa). You are supporting him; he is supporting you and your common goal is your children and a less stressful family life. It wouldn't suit everyone, but it doesn't need to and it doesn't matter as long as you know what you're doing. Maybe the SAHM model works best when both parents feel they are getting the better deal?!!
It's a cost-benefit analysis, and many families feel the benefit of having a parent at home outweighs the cost of the loss of a second income and the cost and hassle of childcare. That's all it is. Just like people may work part-time or a few hours less for the same reasons.
If you're just going to be a SAHM for one year or two, then you will have a good idea how difficult it will be to get back into work. Totally dependent on what you do. Or maybe you have no intention of going back into that field anyway and you are using the SAH period as an opportunity to reassess, retrain or change direction.
There are many things you can do to mitigate against financial vulnerability. I could tell you how we have done that, but that's just us and irrelevant really as everyone's circumstances will be different and different women would be intending to SAH for different lengths of time. People know what's right for them and that's it really.
Yieyr are so many things that can make you financially vulnerable - taking out a mortgage you struggle with; spending or living on credit beyond your means; redundancy; lack of job security; lack of opportunity; geographical factors; mental health; illness; having an financially inept partner; a partner who gambles or who has an addiction; a partner who is financially abusive or secretive; hidden debts - all sorts of things. In any of these circumstances, there is less likely to be a SAHM, put it that way.