If a MUP is useful, I'll probably use it...but most are not that useful.
Example: one of my old commute routes used to parallel the O&E towpath for about 9 miles...but I preferred the road because:
1. Cars are more predictable than early morning/evening joggers, peds, pets, ninjas, wobblers and wildlife.
2. The path is limestone, the road nice and paved. The road is thus cleaner, as well as easier to roll on.
3. The road has the right-of-way over most of the cross streets, the MUP does not.
4. Car headlights and taillights on the road suck less than bike headlights and taillights on the path.
MUPs are built for recreation, not transportation, but if one is useful for you, by all means use it, but don't get your panties on a bunch because some of us ride where we have always rode...since well before most MUPs even existed...on the road.
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"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey