> At least one of my own professors also openly wondered why I was there at all.

I think you completely misunderstood this interaction.

There are 2 possible explanations.

1. You are so smart/knowledgeable that the professor thinks you are beyond college.

2. You were acting like such an arrogant know-it-all that the professor was being sarcastic.

I’ve seen #1, but I’ve seen #2 many times.

You sound like you have a huge chip on your shoulder about not having a degree. I had the same issue at one point before I went back and finished (after working as a professional developer for a while), so I recognize it.

When I did go back, I asked questions in class, I went to office hours to ask questions, and I did research projects with professors. Some back of the envelope math says it would have costs me about twice what I got out owing if I’d paid for an equal amount of time with whatever experts I could find.

My strong suspicion based on the few posts I’ve read is that your attitude is the reason you had such poor interactions with instructors.

I had excellent interactions with my instructors. I interacted with them like human beings and they understood that their limited time would be better spent with students who didn't have the same energy I did. Several professors, when asked, put me through an impromptu whiteboard quiz and said yeah, do your own thing. It's great that you participated in the process in your own way. In my case I asked if I could show up for the final tests and nothing else, because the intermediate work would have been useless, received permission, and passed.

Chip on my shoulder - no, and it's a silly label to begin with. Understanding that it's for other people who value the paper more than intrinsic understanding, yeah.

EDIT: I will concede in some way that I'm proud of not having a degree, and it does influence my thoughts on this topic. I've met some real idiots that do, and I don't consider it a serious differentiator.

Also looking up the thread - at my early jobs, I was surrounded by many people who were interested in educating me on any topic I could think of, because similarly we were all being paid for our time. The difference between that and school was the assumption that we were both motivated and capable.