You're right, and when I say "judging people" I don't mean buying on Amazon instantly means I think you're irredeemably evil, I just mean it's a negative factor in my overall judgment. It can be mitigated by other things, in particular whether the person thinks critically about their Amazon purchases, and whether they take other mitigating action (e.g., voting for government policies that would punish Amazon and similar monopolistic businesses).

What I'm talking about is at least slightly less nebulous than what you describe. My claim is something like "The more that people buy from Amazon today, the lower the expected quality of your own life in 25 years." It's similar to other negative externalities like climate change. I'm not saying someone is satan incarnate for driving their gas car to work. But the less they realize that there are problems with that and the less they take action where possible to mitigate them, the more dubious I'll be about them.

(Incidentally, I'm not "one of those software people who makes plenty of money". I make in the mid five figures with no benefits, so I'm not arguing from quite as privileged a perspective as the one you mention. But my position is still more privileged than many, many other people who can't order from Amazon at all because, for instance, they have no credit card or fixed address. And those people are also harmed by the growth of Amazon as it gradually reduces their options for buying things in person.)