You just skipped down the levels of abstractions in a way that does not address the OP's point.
you see someone say something you find deeply objectionable, like "I support affirmative action in college admissions"
I have no idea why that person thinks that, and can form no opinions about them. Even more specifically, outside a US context they are meaningless.
Contrast that to the OP example:
"Constantly ask yourself why are you working so hard on this damn thing. If the answer is: 'so I can get ahead,' remind yourself that it’s a treadmill and you’ll always stay at the same place, no matter how fast you run."
This is not a statement of opinion about a thing. This is not a "policy is X is good" statement. This is the framework for how this person forms ALL their opinions. This statement could be made by almost any human anywhere in the world.
There are, without doubt, things people can say that give you "a pretty good bead on someone's worldview from even a short excerpt". These are NOT "I support the right to bear arms." They are vey much "I am a strict and devoted Mormon and follow all the churches teachings", or "hard work is all that matters" or "no matter how hard you try, life is out to get you".
If someone can't deduce things about a person from those sorts of first principle short sentences, that is a bit of a worry to me.