* Middle-class Americans consistently pump money into the stock market generically (not information trading), raising the value of all your stocks over time.
* Now you have a gun to their head to support policies that pump up the value of your stocks even more.
* Also, when shit hits the fan, they can't easily cash out, but you can. Both on a mega-scale (recession), and individual stocks (when companies tank, you sell first, and 401k index or diversified funds take a hit).
I'm not an expert in this stuff but it smells from miles away.