All compensation should be taxed. I am not talking about reimbursement of travel expenses, but compensation.
Many of the FT community see FF miles as being "earned." I disagree. FF miles are promotions by the airlines to buy loyalty. Nothing more or less. I have no problem with anyone getting or using them (or switching airlines for better FF benefits). But because someone chooses to spend a lot of time in airplanes, I do not think they are "entitled" to FF miles any more than I am for using a credit card or telephone service that offers FF miles.
As a matter of fact, I could argue the opposite. Selling FF miles to other vendors is very profitable. From what I have researched, the airlines get about 2 cents per FF mile they sell to other vendors. A 25,000 reward ticket, if the miles were acquired only from vendor purchases, will have made the airline more money than if the miles were accumulated from flying. Flying revenues do not cover costs. The miles sold to vendors do.
I am sure I will be beaten unmercifully by many for this post, but I don't care. There will probably be a day when FF programs will all go away and we will all be flying in coach anyway.