Stock market works like everything else, it goes through life cycles. Can't have unlimited growth in a world with finite resources and finite time (from a human perspective).
We grow, than correct / crash and rebuild from there, until the next cycle. Just because he can't predict when this will happen doesn't mean it's not a valid comment, but I do understand the argument of eventually you'll be right if you call it. I just think it's important to recognize it's just a part of life in general including the markets.