By assuming margin you increase your short-term debt service, increase your expected expenses in an emergency and reduce your available credit while being limit

By assuming margin you increase your short-term debt service, increase your expected expenses in an emergency and reduce your available credit while being limited in your access to funds in downturns because of margin calls. That undermines the strategy. In the example, you'd get the same net effect in terms of less-ability to weather emergencies and increased market exposure without having to pay margin interest by just reducing the emergency fund by 1 month's after-tax pay.