Will retiring Boomers cause a stock market decline?

I've seen this argument before: Boomers are going to start liquidating stocks in retirement.

However, if you look at the distribution of ownership of stocks/401ks/IRAs, I think you'll find that a few rich hold a LOT of stocks, enough to live off dividends without liquidating.

The broad masses have little or no stocks and will work longer and/or live off Social Security and home equity. It's only those in between we need to worry about liquidating, those with a few hundred thousand dollars in 401(k)s.

Are there that many non-rich that hold enough stocks to impact the market when they sell? Sure doesn't look like it.

Now sure there are traditional defined-benefit pensions too, but public pensions are still growing and underfunded, and need to keep accumulating. Private pensions are relatively small and hold low stock allocations.

So where is this generational liquidation going to come from? I just don't see it.