It’s terrifying because so many people have retirement funds tied up in stocks and this has the potential to decrease everyone’s trust in the idea of stocks.
For reference, the Norway Oil Fund [1] holds almost 1% of the world's stock which amounts to somewhere in the neighbourhood of 1 trillion dollars. So the overall size of the investable asset universe for pension funds is really large (real estate, private equity, hedge funds, venture funds, stocks, credit/bonds, etc.) and pretty much all well run pension funds have a diversification mandate so there's no concentration in one asset class.
[1] https://en.wikipedia.org/wiki/Government_Pension_Fund_of_Nor...