You're correct in that paying off debts in future inflated dollars would be easier.  The "get out of debt" advice is based on the reality that many people have large amounts of debt, little or no savings, and are dependent on their current income to service that debt.  If they lose their job or their income declines, they have no margin of safety to fall back on and are at risk of defaulting. Also, many more mortgages these days are for the full value of a home, or close to it, and should property values take a dive homeowners needing to sell might find themselves unable to sell for the amount they owe.

I feel comfortable with a low fixed rate mortgage that's less than half the current value of my house, along with a healthy savings account.  If I was mortgaged to the hilt and had no savings I'd find it hard to sleep at night.  Debt in an inflationary environment can work to your advantage, but only if you're still able to make the payments.

I would say the "get out of debt" advice is based on the assumption of relatively low inflation.  It has been a very reasonable assumption since WWII, but it is still an assumption.