Not all SAHMs are financially dependent. And many couples have worked out their financial situation, investments, etc. so that retirement is not a concern.
Most of the concerns I'm reading on here relate to wives being left in a bad position if they have to go back to work/ divorce/ retire. While I agree that CAN be the case, it isn't necessarily the case.
FWIW, my mum was a SAHM (actually she was a SAHW before having kids!) and I have the utmost respect for her.
I loved the fact that at school I would come home to find her waiting for me, we'd have a cup of tea and I'd tell her about my day, and I didn't have to let myself in or come home to an empty house like some of my friends did. She was always (and still is) one of my best friends, and I grew up feeling happy that she was always there for me and we chatted every day about everything.
In saying that it's not my intention to make any working parents feel bad, as I don't believe there is a right or wrong in this instance. I'm just relating my experience.
I grew up ambitious, went to uni, had a successful career, etc. 'despite' her being a SAHM. She was a great role model. She taught me to believe in myself, to work hard for my goals, and that no matter what happened she would be there for me.