Plenty of vehicular cycling advocates (like myself) support bike paths that meet certain design characteristics. Those characteristics are generally consistent with treating cyclists as drivers of vehicles, particularly where traffic control at junctions are concerned, but also horizontal and vertical alignments, sight lines, etc. compatible with cycling at the speeds that make cycling enjoyable and convenient for so many avid cyclists.
Bike paths are also more useful when they create a connection that doesn't exist for other vehicle traffic, or where the roadway connections would be much less convenient. And just as a low-traffic street connection doesn't need to be built to freeway standards, a low-traffic bike shortcut doesn't need to be 12 feet wide. The appropriate design principles for nonmotorized bicycle facilities closely resemble the principles behind road design, because bicyclists fare best when treated as drivers of vehicles.
Vehicular cycling advocates don't oppose bikeways for being bicycle specific; they oppose designs that conflict with normal vehicular traffic control and engineering principles, resulting in greater danger or delay for cyclists than a facility that treats cyclists as drivers of vehicles.