I will admit that the intransigence on the mechanized question has surprised me, and I still struggle to not find the suggestion that skis and bikes are in this respect categorically different just ridiculous. Tom, you have my word that I will keep trying to see both sides here.
Regardless, as I mentioned a little while ago there is more than enough legislative evidence to make the interpretation of bikes as definitively mechanized for this purpose an ambiguous affair. That bikes are outright allowed in some Alaskan Wilderness area is another example which has yet to be mentioned. All of which brings us to your questions about the values-driven reasons why we might want bike access (and paraglider use, for that matter) in various legally protected wild places.
My first goal always has been to get more folks to admit that this question should be considered on a case by case basis. The JMT will remain a great catalyst for discussion because the management issues it faces are so egregious. If principles will work there, they'll probably work anywhere.
Let me use the Glacier/Bob Marshall area as an example, both because I know it well and because the Bob is somewhat unique amongst the larger, older Wilderness Areas in that it has a lot of relatively low elevation, gentle terrain.
There are almost no trails in the greater area which would be bikeable December through April due to snow.
There are some trails, chiefly in the park, which when snow-free are too crowded for mountain biking to be practical. Perhaps trails like the Highline and Siyeh Pass could be open to biking only in the late fall during the very narrow (and often non-existent) window when the road is closed to cars but the trails are still free enough of snow and ice to ride.
There are many trails, chiefly on the western side of the Continental Divide, which are very muddy well into July. Biking on these would be a bad idea, though even if they were open year round the mud is such that you'd get few takers. Keeping them closed to bikes through July 20th might be a practical compromise. Naturally, stock can go on these whenever they please, and if it weren't for this the mud wouldn't be so bad.
There are a large number of mid and high altitude trails, which get varied use volumes, which are sufficiently brushy well into August that riding a bike would be rather challenging. Indeed, as with the mud very few would elect to ride these if they could. This vegatation gets knocked down by a combination of summer heat and late August frost, and is typically mostly gone by September 1st. In Glacier in particular, I'd have no quarrel with the bike season on many/most trails being limited to a two month window in September and October (and perhaps November, snow permitting).
There are a few trails in the park, and a lot in the Bob, which have a rocky tread which drains well, and are not heavily used. These should be open to bikes year-round. On a handfull of these conflict with stock could be an issue. Two management provisions would be necessary here: a rule which would limit the number of pack stock per guest for outfitters to 2 or 3 (I've seen pack-in raft trips which had 50 mules for 5-8 guests), and a strong message from the various FS offices to said outfitters to get over it. This last is all but inconceivable at the moment, but rolling back the power stock-based outfitters have in the Bob is vital regardless of whether bikes are a part of the conversation or not.
There'd be lawsuits about the potential effects on Grizzlies and moose, and the whole affair might even lead to a productive conversation. Eventually.


