Goldenbear, "hardest job in the world", "most important job in the world", "24/7, no breaks" - this type of drivel is pervasive, both in MN (to a lesser extent) and in real life.
I don't know about you, but I don't hear any other group claiming this about their occupation or role. All jobs have their stressful parts, most have at least something enjoyable about them, others have high levels of difficulty or barriers to entry.
There is no "it is a fact that you are doing additional work in the day". SAHPs don't necessarily do anything extra than a working parent doesn't do. SAHP with kids at school can quite easily use this as leisure time. SAHP of any age children can have staff to do cleaning and childcare. SAHP can be run ragged with demanding kids or can have a pretty chilled out lifestyle. It all depends on their individual situation.
I don't see anyone here telling you to get a job, Goldenbear. If you wanted a career, I'm sure you'd have one.
In most circumstances, and barring disability, I tend to think, 'so you just don't want it badly enough? Fine, but not the same as can't.' If not working suits your situation, great. Embrace that. Enjoy your role for what it is, don't make it out to be something it's not. And if it doesn't make you happy, don't be a martyr, change it.