One reason why not would be for some necessary avoidance of disclosure to you, which would have had to have been architected by something that is not you, otherwise you would have known about the thing you couldn’t disclose. If something exists that is not you, then solipsism fails.
I'm not saying everything is made up in my mind like some sci-fi movie plot. I'm saying that we're confined to the limits of our perception and beliefs in a very real way. Maybe it's all in my mind, but that's somewhat different.
How about this: people's memories have been shown to be somewhat malleable. Framing a question with subtly different wording or prompting with an intentional nudge (police officers do this) can warp the witness' perception. There may well be some objective truth about the incident and maybe someone knows it, but for that witness, their world has diverged.
In the extreme case, someone who is very deluded can't process the truth that the rest of us can see. But do we really see the truth, or is it that we brand what we each see as the truth? Maybe the deluded person is right. Even assuming you are your own person entirely, I don't seem to be able to connect with your world with absolute clarity. Maybe technology can change that. If you are a figment of my imagination, well, I can't tell.
As you’ve said, perception has been demonstrated to be subjective, even controllable by others. There are layers of this including individual (introspection and observation) and collective (cultural relativism, emic and etic perspectives), etc. I agree this is something that is very helpful to understand.
Truth, likewise, is a murkier concept than many people realize or want to think about, and the relative contexts literally determine what is true and not. I also agree this is helpful to understand.
Your last sentence is the only problematic bit. In a limited effort, it is easy to casually say that you can’t prove anything beyond your own perception. But this statement is much less likely to be functionally true (and things like evolution only act on function). This statement, taken seriously, and extended, unlike everything you’ve said prior, can be very damaging, because it presumes not only are we each different, but that you are the only real one, and thus your own perspective is literally the only one that matters. It isn’t hard to see why this is not a good perspective to hold in the large majority of cases.
I don't believe only my perspective matters, and I don't think anyone should. I use the term "subjective reality" so heavily because it is scoped to each person and it is their reality. I can't truly know if everything is in my head. That also means that, for things I perceive as not in my head, they are functionally external to myself. The fact that I have these boundaries of whether I genuinely and completely think something is in my head prevents my subsumption of other perspectives as my own. In this HN thread, I have no choice but to engage you as one human to another, because if I've already thought out your responses and this is just a dream of sorts, I can't tell.
