'My point was that I don't think it's such a stretch that feminists would argue that being a SAHM is not a real 'choice ' but just acting under the influence of patriarchy, just the same as they might say about leg shaving.'
Again, this doesn't amount to 'not knowing your own mind.' Every single choice a human makes is constrained by the situation they find themselves in - not a single choice is 'free' - everything has events leading up to it and consequences following on from it. I can only choose to eat a sandwich today if a sandwich is available, I can buy it, I'm not allergic to it etc etc etc. Every choice, no matter how tiny, has a massive web of circumstances around it. Understanding the web of circumstances around the choice to be a SAHM isn't about who knows their mind or not, it's about understanding the processes that lead to, for example, far far more women choosing to stay at home than men, and the consequences of that imbalance. There isn't a value judgement involved about how well someone knows their mind - each individual woman does whatever works for her at the time - but understanding the bigger societal picture makes it more likely that fewer women will find themselves in situations where they don't actually have a choice (eg because they can't get flexible working, because they're controlled and pressured into it etc) or where the consequences of that choice are dire (eg not having any financial security).
Staying at home to look after children is a worthwhile activity - it'd be very hard to argue otherwise, given that children are essential to continuation of the human race and someone has to look after them. However, in our capitalist, patriarchal society being a SAHM isn't valued at all and for the woman herself, being a SAHM can leave her very vulnerable. This absolutely should not be the case and so understanding why that situation has arisen and seeking to change it is a positive thing, something that feminists have worked for for a long time.