I don't think they will pull out. That's what's driving the prices so high.
If everyone just lets money go from their check to the S&P 500. And most of that is flowing to only 10 companies. I think about it, if 3rd of the market is blindingly putting money in every month and a 3rd of the market isn't selling an equal amount it will send prices up.
The problem is when it's time for Baby Boomers to retire en mass and they start pulling money out. Huge bear head wind.