Debt is a useful tool for people who can control themselves.
Dave Ramsey caters to people who need unusually strict financial discipline to avoid getting in trouble. For everyone else, responsibly using debt is often better than paying cash.
For example, paying cash for a car is often worse than taking a low-interest loan. Liquidity is important -- locking up a bunch of money in a car means you can't use it for other things, like investments or emergency savings.
Another example: taking out a loan for a large purchase, rather than liquidating investments to pay cash, can cost less overall because the interest paid on the loan might be lower than the capital gains taxes on the investments.