I don't think it's appropriate to bash an oversized vehicle through places it has no business, widening trails and knocking down features and trees.
And so long as we're talking about established roads, built for vehicular traffic, a full size should fit without any issue (other than pin striping).
Where I live, the trails/roads are very tight and heavily vegetated, arguably more so than what I've seen out west. The full size trucks I've seen go down them certainly aren't knocking down features and trees. At most, they're breaking off a few over-hanging branches, which would've needed trimming anyways. It seems like you're trying to build up a controversy where none exists.
Stuff like the Rubicon and Black Bear are established roads, sometimes these "trails" are dual listed as FS and county roads.
Yep, and we've already established that full sizes have made their way across some of those types of trails without much drama.