Thank you for giving your reasonable thoughts on this. The issue with your approach is that there's a diverse range of content and if the players can only see what was available in the ISA, they wouldn't know that there's alien content as well.
The demo is however meant to be short, taking the player from NSFW scene to NSFW scene. I think there are about 7-8 NSFW scenes available right now in the demo, and each of them is supposed to hint to the player what they can actually expect in terms of NSFW content, which wouldn't be possible if only one chapter or two chapters as you say was/were available.
No NSFW scene should really be censored in the demo as it is, so I'm not sure what you mean by this. There are descriptions in-between memories as to what might have happened so the player gets an idea of what other scenes there could be.
Most people coming to this game will be here for the sex, and if most of that is removed and/or censored, they won't be able to properly form an opinion on said content.
The saving being locked, that's inspired from a demo of a very successful game, but it's not just a "personal choice", it's also a technical need because the save the player could make when they're teleported across the game to see different scenes would likely have bugs when loaded in the full build for example.
I'll think about it, maybe the demo for the Steam build will be different. If you're a solo dev and you try to provide an incentive for people to support you in getting anywhere near completion of the project, you have to try different ways because as it was the public builds weren't really doing anything at all, because people could just wait.