First, even if you couldn't pay off your mortgage today that doesn't mean you would be in a bad position at all. If you had enough to contribute 50k a year (plus job increases) and had 500k left on a house you would be in great shape. You would be happy to have the debt and the entity issuing you the debt would be happy to be repaid.

Second, while it is useful to think of debts in terms of things like mortgages and auto loans, most of this global debt is government debt. Think locally - your local town may need 50 million dollars to build a new school. They aren't increasing taxes for one year to build the school they instead take on 50 million dollars of debt in the form of bonds. So even if you have no personal debt you still have tens or hundreds of thousands of dollars in debt which the government has taken out which can reasonably be repaid overtime.