First off, I'm not going to sit here and prolongedly argue the points made by a man long dead in an age when this sort of language was acceptable. Second, I want to make clear that my use of any term equating weakness in no way has anything to do with the specific context that Stevenson used.
Like I said, I agree with Stevenson's basic assessment in his beginning paragraphs:
A man who must separate himself from his neighbours' habits in order to be happy, is in much the same case with one who requires to take opium for the same purpose.
Thoreau quite obviously was an escapist, a naive idealist, both in the regard he showed for nature and in his politics. He wanted to cut ties with what he saw as the more problematic proclivities of human society. Thoreau shunned alcohol and caffeine, not wanting to mar the purity of his perception. Stevenson scoffs at his "moral shyness" calling it "delicate." I'd call it tedious. I'm skeptical of anyone who erects walls without gates around their basic appetites according to some arbitrary philosophical conclusion; in my experience, it's usually indicative of control issues of one sort or another, barring oneself from the possibility of an indiscretion.
If you haven't already guessed, I'm not a big fan of Thoreau as a writer. I tried to read Walden years ago, I just couldn't get into it. I lean more toward scientifically descriptive literature regarding nature and not because I'm a cold, dead hulk of data processing either; I think it has a lot to do with the fact that I've spent so much time at my grandfather's cabin in Western PA. My family would spend entire summers up there. For several years my father would take all of his vacation over those summers and spend a solid month. You don't see other people if you don't want. You're surrounded - literally - by trees that have been growing for over a hundred years, since the house was built. It has electricity and a sink inside, but that's about it; the shower is on the side of the house and the outhouse is far enough away to make midnight trips to the restroom uncomfortable. Thoreau's discussion is too familiar.
That's all personal, of course. The man is an icon, and his work has inspired and molded environmentalists for over a century. This is where history proved Stevenson wrong; Thoreau might have preferred escape, but that's not what happened. Any discussion of the genesis of environmentalism is incomplete without Thoreau's influence. Surely there is strength overflowing in the man's work to have such staying power.
It's interesting that even so early on the primary criticism of environmentalism was the inherent weakness of feeling affection and a moral obligation to something as inhuman - or "unmanly" - as the desire to be closer to nature. I understand the line of logic that forms this critique in that time period. A hundred years before Thoreau, American was wild and dangerous. Nature was a foe for settlers to conquer, constantly trying to reclaim and drive out the invaders. It's safe to say there were no environmentalists with a burning desire to protect back then; urbanization and comfort forged the modern nature lover. It must have been strange to see this almost traitorous trend to connect with and nurture the very enemy that until recently withheld prosperity from Americans.
The inhumanity of nature is described derogatorily using words that denote womanhood, which is also nothing new. In all mythology, not excluding Abrahamic religions, women symbolize the earth, they embody nature as the vessels of new life. I'm not going to delve into Jungian psychology, but these ancient perceptions were a part of the reason why women were pigeonholed in this period as mothers and homemakers who left the "strong" work to men. So the framework of distaste for environmentalism was established hundreds - if not thousands - of years before it was applied.
I'm going to split this in two parts - maybe more - because I want to really give the change in ideology, resources and public perception a good look in the 20th century.
The sun is shining outside. I'm going to go have an unmanly afternoon in the park.