Well, you're not exactly a "sample size one".

When you say "a lot of people" you also presumably witnessed, interacted with, talked to, and watched, other people that do the same.

I can e.g. say "a lot of people have iPhones in NY" just from walking around in Manhattan, even though I never read any particular study.

Seeing people and seeing that many of which you see everyday do X is still sampling.

Yeah, but I would think that humans are generally bad in "intuitive statistics", e.g. when drawing conclusions based on their observations. Of course most of this may come from our inability to observe accurately/objectively when not dedicating significant brain-power to this task.

aka the https://en.wikipedia.org/wiki/False_consensus_effect

This sort of empirical determination of different groups of people's "intuitions" may be interesting social science, but should it really matter to philosophy? Shouldn't terms just be defined carefully enough that intuition doesn't come into it?

Concepts like "justice" are just social constructs and not aspects of the Universe that exist outside of humanity. They will always be arbitrary.

differentiating fact from speculation is a difficult and important venture that requires vigilance throughout one's entire lifetime. It's very hard, and we all slip up because it's not really how our brains like to work.