You may have mortgage debt for a while but it’s NEVER good to have debt. I don't want to back talk your dad because outside of this he may be a wise guy but his response is based on the following.
1) You will always have a steady income. I think our current economic state proves that this is not true. Also, if you have any outstanding debt that is not paid then you forfeit the possessions (house, car, etc.) you owe money on. The only way to guarantee that repossession doesn't happen is by paying the debt off.
My parents failed to pay off their meager mortgage ($24,000 home) because they felt they needed a tax write off. Eventually, they expressed a desire to have my brothers new suburban home. My brother offered it up and they bit but the old house was still not paid off. My brother moved into the old house but lost his job. He missed a few mortgage payments and the house was still in my parent’s name. If my parents had paid off the home when they had the money then there credit would not have been dinged.
2) Auto debt is good. AUTO DEBT IS NEVER GOOD. Automobiles are the absolute worse drain on your income. I am from Michigan and auto sales have helped put food on my table but the thought of a car note costing $500 makes me sick. If you add the cost of gas, maintenance, registration (Mine was $107 this year), and insurance then you will want to projectile vomit. My car is paid off and the thing still costs me $300+ a month to maintain; all this money just to get from point A to B. Furthermore, my wife and I only own one vehicle and her job is less than 10 miles from the house. I work from home and only travel to the office two-three days a week. I can't imagine what those who have two cars along with driving a long distance to work pay.
A side point: Consumer debt is the worse from a behavioral standpoint. I felt horrible even putting $1,000 on my credit card even though I KNOW that I will pay it off and have to pay no interest. Why? I don't want to get into the HABIT of buying now and paying later. Delayed gratification always makes your purchases and economic progress feel better. Also, delayed gratification is the key between living debt free as opposed to having debt. Unfortunately, once the habit of instant gratification is established then debt snowballs.
A huge post to conclude that debt is bad. You don't want to owe anyone. Planning, patience, and delayed gratification will help you to live debt free. Add long term investing into the mix and I believe you have a formula for getting rich slowly.