Professor Gros himself says almost nothing of Whitman, though he does say plenty of Thoreau. Our popular notion of the latter is of a hermit-like solitary individualist, a guy not even invested enough in the society of his peers to pay his taxes when disappointed by his government. From a Gros point of view maybe that's fair, so maybe we can't infer his take on Whitman from what he says about the author of Walden.
Seems to me, though, that Whitman's famous "barbaric yawp" in celebration of the teeming masses of Manhattan is not so different in tone and intention from Thoreau's more secluded call of the wild. Both are declarations of attachment and an expansive sense of identification with a larger world, and with a nature whose constituents include varieties of organic and pan-temporal life including but not restricted to humanity. Both, in their different ways, affirm what William James called "our really vital question... what is life going to make of itself?"
In discussing Proust, Gros - in his oracular style of un-circumspect pronouncement - says "I refer to the stroll [or promenade] as light relief, relaxation, walking to 'get some fresh air'... you say goodbye to your work." But I think it's not so simple, so architectonic and neatly boxed. When strolling with children, as discussed yesterday, the work/play distinction simply does not arise. The adult stroller who is open to the instruction of children (which can run in both directions), the Thoreau-style saunterer who always "walks to work" like D.B. Johnson's Henry realizes that real work is too important to leave at the office desk.