I don't see how it's inconsistent with MMM to point out that there are factors which are, definitely, making it harder for the middle class to get ahead or even stay even. You say that the type of housing is a choice, but you're looking solely at the price of buying a house. Rental prices are going up as well, due to those very same costs for land, but wages haven't been going up. So it's harder and harder for poor people to find affordable rentals. Many of them get pushed out of the urban areas which are closer to a greater variety of jobs, and out to where public transportation is crappy and takes a long time to get anywhere. Thus, they depend on their vehicles to get to their job or jobs, get children to daycare (which is incredibly expensive and the most affordable daycares are almost certainly not anywhere close to the job/jobs), and get basic foods, since those places don't generally have grocery stores.
It's all very well for us to sit here from a position of affluence and say, "Get a bike, slackers!" but we have options. If you're having a hard time making ends meet every month and you've got $20 left with a week to go before you get paid again, are you going to use that money to buy a used bike off Craigslist, or are you going to use it to feed your kid? Even if you do buy the bike, that doesn't solve the problem of how long it would take you to get to and from work--time cost--or the fact that it only transports you, not your child. Buy a bike trailer! Oh, wait, you don't have money for even a used one. Whoops. And neither do you have money for food now, so look into your hungry child's face and say, "Sorry, kid, looks like you won't get to eat."
It's the same with cooking. Cook at home if you're so poor! But, so many people lack the basic skills to know what to do with food. It takes time to learn to cook, time which poor people frequently don't have, and having someone show you what to do is usually the best option. If you tell someone who's never been shown the way to cook, "Saute that onion," they'll have no idea what the heck you're saying. I'm lucky. I've been baking on my own since I was 12, because I have relatives who love to bake and showed me how. My mom showed me how to cook. My husband's mom showed him how to cook. Not everyone has that in their life, however. Heck, telling people to cook even assumes that they have access to the means of cooking. In my current apartment, the stove has a burner which died over a year ago and the landlord tried to fix but couldn't. So, we've had to live without that one burner because buying a new stove is off the table. Sucks to be us! And our landlord is pretty decent. What about slum lords? Do they really care if their tenants have working ovens? If you tell someone to buy a slow cooker, they might run into the same problem as the bike. Yay, they've got a slow cooker! And no money left to buy food to go in that slow cooker.
"Having kids is a choice", you say, but birth control fails, even when it's available and used correctly. I personally know of several children who were part of the .1% improbability, and even a few kids who were assumed to be an impossibility after the couple was told that they were infertile. "Get an abortion" is becoming less and less of a possibility thanks to the very same politicians who think it's "fiscally responsible" to cut services for the poor. Besides, what's your advice after the kid is born, go back in time and not have the sex which created that life? That's assuming that the woman in question even had a choice about the sex to begin with.
There are so many factors going into your financial circumstances that you never even think about. Be grateful if you do have the skills to do what you do to save money. Be grateful that you have options. And try, if you can, to remember that you've had a lot of help getting to where you are. Even better, support people who are trying to make the world a more equitable place, as Ms. Warren is. Why is it so shocking, or so unmustachian, to point out that almost all of the economic gains in productivity over the past few decades have gone to the already rich? Yes, there is over-consumption and we can all point fingers at people who were their own financial downfall. But there are also a lot of good, measurable reasons why it's harder to get the basics of life now. Again, how is pointing that out "unmustachian"?
There's a huge tendency on this forum to conflate "my life experience is X, therefore everyone else's experience must also be X and if they're not doing as well as I am then they're just lazy and/or stupid". Your life and circumstances are unique to you. Do not confuse your truth with universal truth.