Most critical? Maybe not. But it is undoubtedly very much a significant and underrecognized factor.
The Overview Effect is a real thing: https://en.wikipedia.org/wiki/Overview_effect
At its best, it inspires calls to environmentalism (the fragility of the Earth), but at its worst, and it's usually at its worst, it inspires nihilistic Carl Saganisms like the Pale Blue Dot.
To me, at least, it's less of "how could anything here matter when Saturn is so big?" and more of "does it really seem plausible that this vast universe was created for the benefit of some creatures on the surface of this little speck? Do you really think we're that special?"
Certainly it's possible to ride the Overview Effect all the way to nihilism, but it seems clear to me that unexamined anthropocentrism is at least as incorrect.
One is a short-lasting altered state of consciousness.
The other is an idea, a change of perspective that can inspire action and positive lifestyle change. Or perhaps a descent into nihilism, depending on circumstance.
