In order for you to pay off your mortgage, you need to receive money. That money was generally created through the creation of debts.

So it is hard to say exactly who took on that debt, but someone probably did.

For more on how debt creates money, read up on http://en.wikipedia.org/wiki/Fractional-reserve_banking. And the person you replied to is exactly right - our entire economic system only works right if there is a lot of debt to go with it.

Paying off a mortgage destroys debt (and therefore, the money you used to pay it off).