How do all you working mums know what us SAHMs talk about? You're not usually there...
What we actually say is 'God, those deathly dull working mothers, all they ever talk about is how tough it is for them, and how nobody understands them, the guilt, blah bah, glass ceilings, the boss gets the hump if you leave at 5 on the dot, the child-minder gets the hump if you don't, having it all is a myth, the guilt, blah blah, quality time, work life balance, my child is more sociable and well balanced for having been in full time day care since he was 3 minutes old, more guilt, blah bloody blah. SAHMs aren't the only ones with a cliched existence and limited conversation!
Don't keep looking for ways to justify your choices and don't expect OP's friend to need to justify hers. It's hardly her fault that she's got more money than you is it?
Some of us are hugely dull and shallow, some are very fulfilled and happy at home despite being highly intelligent and capable in the Real World, and some of us are going out of our minds with boredom, but we genuinely believe that we are doing the best thing possible by staying at home. Either that, or the logistics of going back to work negate any benefits, financial or otherwise.
Personally I get a bit hacked off with those WM's who insist on telling anyone who'll listen how tough it is to be them. They love to think all SAHMs live in a deluded smug little bubble with no understanding of the cut and thrust of the grown-up world. Maybe some of us do, but I just don't care enough that so many WM's want to get their knickers in a twist over my lack of interest in joining their ranks. After all, none of them make it sound very appealing, frankly.
If you don't like your situation change it. And if you honestly can't change it then don't waste your energy getting bitter and twisted over people who appear to have it better than you. Things are not always as they seem.
Years ago, when I had a toddler and a new baby I sat next to a very ambitious successful WM with a small baby in full-time day care at a dinner party. She asked me why I chose not to work, and I told her, (somewhat naively)and without a hint of militance or prejudice, that it didn't really make sense for me to work as I had no particularly riveting career to get back to, and as we were managing fine on one income the hassle involved didn't seem worth it. She smiled sweetly and told me how lovely she imagined it must be to stay at home and bake apple pies all day. (yes really!) She then went on to explain how she wished she could be the 'type' to be content with that, but property prices in her (very chi-chi) part of London were extortionate, and she could never live in the suburbs as she'd go out of her mind with the bland naffness of it all.
From that day on, if anyone ever asks me why I don't work I reply very clearly, and without the need to elaborate: 'The ONLY two reasons; Don't want to, don't need to.'