Just pause the game.
Any game without quicksaves should at least have a “save and quit” option. So you can quit without losing your progress and when you get back on it deletes the save, so no save-scumming.
As a complete non-gamer (well, on consoles; I play a few PC games, but never online ones), can anyone else use the system if you do that? Play that specific game on their profile? For people who live with people and share a gaming system.
On the PC, it’s hit and miss. Some games react poorly to Alt-Tabbing out and will lock up either the game or the entire system. Playing a second game can be problematic because the first game can be hogging resources. Really though, the main issue that there’s no guarantee that you’ll be back in five minutes – you could easily find yourself returning later and realizing that now you don’t have the time to devote to reaching the next checkpoint so you either pause again for however many hours or just give up and turn it off. I don’t think any consoles have the capacity to switch between active games; your Xbox is just stuck paused until someone ends the game.
Enalzi make a good point for a solution although, honestly, I can’t imagine the state of affairs that leads someone to get upset that someone, somewhere, might be playing a single-player game differently or “wrong”.
I guess it’s not checkpoints that bother me, per se. It’s the fact that you only have 1 save file. That’s what is forcing me to choose between abandoning AC: Revelations, or starting it over from the beginning.

I guess it’s not checkpoints that bother me, per se. It’s the fact that you only have 1 save file. That’s what is forcing me to choose between abandoning AC: Revelations, or starting it over from the beginning.
How common is this? It is rare that I play a game with just one save file.

I guess it’s not checkpoints that bother me, per se. It’s the fact that you only have 1 save file. That’s what is forcing me to choose between abandoning AC: Revelations, or starting it over from the beginning.
I wonder if you could C&P save files and save them in a different file?

I don’t buy that it’s that hard to save where you are in modern games, due to all the space we have. You’ve got the save file basically in memory–it’s just the state of the game. Reducing that down should not be a hard problem. Sure, autosave can be a nice bonus, but there’s no good reason not to be able to keep your position on a map and the state of the game. You’d need the latter anyways for autosaves.
I do get getting rid of save points. They are less convenient. But allowing you to save as you quit? That’s not inconvenient at all. It’s a simple additional question. And you can still have a timed autosave, just in case. (Though do keep it in a separate slot, in case the save happens at a really bad time.)
Speaking as a professional game developer, this is WAY harder than you make it out to be… particularly if your game systems were not designed to be easily saved-and-restored from the beginning.

How common is this? It is rare that I play a game with just one save file.
All the games I mentioned in post 14 were like that. Just Cause 3 is another open-world action-adventure game I forgot to mention that’s like that.

I wonder if you could C&P save files and save them in a different file?
Probably, on a PC, but on a PS4 I don’t believe that’s possible. What I think would be possible is to periodically back up the save file to USB device; then, if I ever needed to go back to that save, restore it, overrwriting the then-current save file on the PS4.
Having just YASD’d a wizard that I was really doing well with otherwise, it’s a reminder that uncontrollable saves and permadeath have been around for decades. (Yes, I could have save-scummed, but I really want to ascend legitimately once in my life.) Of course, the OP is right that there is more of a trend in modern games to get rid of manual saving.
But I’ve dealt with all sorts of save systems. Ones that don’t actually save, so write down this access code to start at a particular level. Ones that let you save anywhere from a menu, but only have a few slots. Ones that always require checkpoints but don’t autosave. Ones that require checkpoints but do autosave. Ones that let you save anywhere, but never autosave. Ones that do both. Ones that make it impossible to manually save.
I think they all have strengths and weaknesses. I’ve lost hours in games like FF7 by forgetting to hit a checkpoint and then dying. The newer Fallout games let you save anywhere but the save files get absolutely huge. New Vegas on PS3 was bugged so that eventually you’d get terrible frame rate drops where the only cure was to create a new save file and quit. I don’t know how many characters I’ve lost in NetHack. Saving in platformers can be anything from saving at a central hub or world map but not in levels to manual saves anywhere to autosaving at invisible points with area changes. Some people swear by Ironman in X-COM, while others like being able to try again. 4X games tend to be a combo of multiple autosave files and manual saving.
Suspend mode helps, but I don’t trust it. I’ve had too many games eventually fail to come out of suspend on my PS4.
Even on a PC, backing up saves can be finicky if you’re not completely sure on what you’re doing. Plus stuff like Steam cloud saves will want to overwrite your restored save. It’s not impossible and I wouldn’t even imply that it’s “hard” but it’s not always a matter of adding or deleting *.bak to the save file either.