Alan, I really liked your rebuttal to the Columbian letter to the editor. I don't see how you can get it down to 200 words, it's all very good info!
I would suggest going for the meat-and-potatoes:
"Bicycle sales are taxed, just like car sales. Bikes don't pay license fees here, and most everywhere that has tried licensing bikes has found that any appropriate fees do not generate enough revenue to pay for the bureaucracy needed to administer and enforce the program. (For example, San Jose recently stopped licensing bikes, and there are many other examples of places where it hasn't worked.)
Moreover, automobile user fees (fuel tax, registration, tolls, etc.) cover only part of public road costs. For federally funded roads, about two-thirds of the cost is covered by user fees, the rest comes from general funds paid for by all tax payers. Car user fees cover an even smaller fraction of local roads, for example in Seattle, gas taxes pay for roughly four percent of road costs. Registration fees go to WSDOT for state roads, not cities, and again don't cover anywhere near the total road budget. So, we all pay for roads and those who don't drive or drive less (such as some who ride bikes more) end up effectively subsidizing those who drive more. "