Why is the morality of miles any different from the morality of life. If you will cheat an airline/hotel/rental car agency why won't you cheat at everything? Taxes, girlfriend/boyfriend/wife/husband/life partner/steal from your employer, etc. Either you are an honest and moral person, or you aren't. A rose is a rose folks and you're either honest, moral and ethical or you're not.
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What would you do if you weren't afraid?