hi Sourdough -
first of all, Indian Arm is not a watershed. There are watersheds near the Arm, but the arm itself does not provide drinking water to our municipalities.
Second, we Vancouver citizens owe enormous gratitude to the gargantuan and largely uncredited efforts of individuals such as Don McPherson
(builder of the Indian Arm trail, and of the Grouse Grind before that), Halvor Lunden
(Diez Vistas, Eagle Ridge / Lindsay Lake / DD trail and many others) and James Cunningham
(an ordinary stone mason who took it upon himself to build the Seawall around Stanley Park on weekends, over 30 years !!!)
These, and many other individuals, built structures without a bid process, without tender - yet, we use these trails and structures every day, and they appear in Tourism BC brochures and maps to encourage tourists to visit our town.
I don't think it's fair to accuse Don McPherson of 'creating his own recreation' when (1) 99.999% of Vancouverites will never even think of attempting this route, and (2) 99.999% of that remaining 0.001% will perhaps give it a thought, then turn to a less challenging trail.
As for animals, they know how to safely cross a man-made trail during their migratory and other activities.
Finally, you appear to regret that this trail was ever built - yet I cannot fail to notice that, in your closing paragraph, you mention a desire to hike it.
See? It's not so bad that it's there after all, now, is it?
cheers - C Wall