Middle class as defined by Investopedia:
Individuals who fall between the working class and the upper class within a societal hierarchy. In Western cultures, persons in the middle class tend to have a higher proportion of college degrees than those in the working class, have more income available for consumption and may own property. Those in the middle class often are employed as professionals, managers and civil servants.
I think what happened, is those below this were targeted to be "brought" into the fold. If you look at most of the foreclosures on homes and people in trouble, they were the first to be introduced to the money by proxy. Take equity and spend it. Making us look more like the diamond:
That being presented, it should not surprise that this was an indirect effect of the progressive tax and tax code. Believe it or not it's the personal/dependent deduction that take the biggest chunk of taxabale income and turn it "untouchable". Case in point, I have a co-worker salary $125K/yr, of which his deduction of himself, wife, and four kids (+child credit), 401K investments, mortgage interest, and all other deductions drop him down to to almost 60,000 AGI.
$65,000 untouched dollars.
Now, ask yourself the question, is he middle class? The original definition describes him to a "T". But definitely, locale will determine levels of course, but as civil servants, we all know the "adjusted" income we receive because of where we live.
So, if we brought "up" all these people who normally wouldn't owned property, inflated values, validating their salary on "future" worth, then yes....Somebody sold them a bill of something that stinks. Hence the bubble was constructed, filled, and then popped by the unscrupulous investors.
The same way the "DOT COM" bubble was created and popped. Venture Capitalists. I remember the SEC doing the audit on my firm that went "public" and realized it was nothing more than "kicking the tires". Government oversight that failed miserably.
Any way, middle class, yeah, we need a better term. Bubble? yep, popped a few years ago....