Systemic problems require systemic solutions. To preempt an obvious rebuttal: shaping the landscape of choices that are available to consumers is literally how markets work so it's not like libertarians or other "free" market fanatics have a high horse when we introduce ideas like regulations on corporate behavior.
> if everyone puts their money in the same place then companies get too big and distort economies.
You're not going to make the big companies smaller or prevent market distortions by doing this. That's what I was referring to by "move the needle."
I think beyond a point govt should just buy a stake in them. That would keep them from misbehaving too much. Which is what happens in China, India, Brazil etc cause otherwise large poor populations will just be pushed out of markets.