Using Credit Cards For Airline Miles?

Dave's response takes flight as he explains why using credit cards for airline miles are a bad idea.

Question: Bobby says Dave should not call people who use a credit card for groceries losers.  They may be using the card to get airline miles.

Answer: According to Dun and Bradstreet, consumers spend 12%-18% more when spending with plastic.
Consumers spend 37% more at fast food restaurants when using plastic.
Consumers spend 78% more at vending machines when using plastic.
Consumer reports say that 78% of airline miles are never redeemed.