Okay, Seanto and MordBass, you two seem to have taken up the banner of "ghosting and coming back from it to ask for something as though it never happened is reasonable," so I have some follow-up questions. I hope you won't take them as aggressive or judgmental. I'm totally just curious.
You share a certain skepticism of authority and expertise...
OP thinks that they are somehow reinforcing a universal standard of professionalism
I got a feeling of "I have oh so generously bestowed wonders upon you, hare dare thou not appreciate it."
...which is not in itself confusing. What is confusing is the idea that you would not try to manipulate this system to your benefit, even if you don't take it seriously. Like, even if your boss or teacher is an idiot who doesn't deserve their position, if you need something from them, wouldn't part of trying to obtain that something involve trying to get them to think well of you, in part by expressing (in this case inauthentic) respect for their expertise and authority?
Seanto, when you say:
Yes, i would give an unreliable person a good reference, because the whole system of it is bullsh*t anyway.
...is this something you would directly say to someone from whom you wanted a letter of reference? Would you be surprised if saying this affected your likelihood of getting such a letter?
Mordbass, your question:
Are you really going to hold somebody to the one bad thing that they did in a position that was ultimately voluntary and unpaid?
...cuts right to the heart of the matter: For you, it seems that suddenly blowing off a bunch of people who are relying on you, severing all contact with them, and not offering them any explanation, even later when you come back and want something from them, is minimal enough to be called "the one bad thing they did." From my (and I expect the OP's) perspective, ghosting like this, however common or "normal" it may be, seems like it must include the assumption that the relationship will be seriously damaged, if not destroyed, and that if it can be patched back up, it is likely to require a lot of work on the ghoster's part.
Again, this is so far not confusing, just a difference in position. What is confusing is that you would not suspect that the person from whom you want something is likely to take this second position and you are going to have to overcome that difference before there is any chance of getting what you want.
So, for example, when you tell this story...
I abandoned a job once when I was younger because I had just gotten to work and suddenly had a massive panic attack... I didn't owe an explanation to anybody at that job.
...if you had showed up after 3 days, 3 months, or the full 2 years, and started about your daily tasks without comment, would you expect nothing to be said about it? Would you be surprised if your boss said something like "*** dude? Where did you go? What happened? You don't work here any more and, unless you provide a satisfactory explanation, you can't have your old job back!"?
Seanto, you present an interesting worldview that serves to explain some of this here:
If someone ghosts out on me i generally am not mad at it or think that some sort of justice needs to be served. I just go on with my life and assume they did it for a good reason. Nobody is truly obligated to be my friend or fulfill their commitments to me and that is OK and i will reciprocate that feeling. Way of the world.
...But you say "generally." I am curious to know if there are individuals or relationships in your life in relation to whom this would feel like this was a big deal? Do you have parents, siblings, children, SI, or best friend who, if they agreed to meet up with you but instead suddenly disappeared from your life and refused contact with you for months, and then they showed up at your door and acted as if nothing had happened, you would do more than shrug?
Again, I hope you both take these questions in the spirit of naive inquiry in which they are intended.