you have a horrible situation very comparable to 1929 (in terms of vulnerability to a crash).
As I've stated several times ....Testing recent lows ( even testing S&P 4,000 ) is a distinct probability . A crash ala 1929 is very very unlikely .
Where I could be wrong . If Russia decides to block all gas / oil exports to the EU ..oil would probably spike to around $180 a barrel and most world economies ( excluding the oil exporters ) would fall into a very several recession . That and Russia using nuclear weapons in Ukraine .
Margin debt levels alone is not enough to cause a 1929 type crash JMO Kiwi