Ovinomancer
No flips for you!
Man, that's a gish gallop. Did you want to toss in the kitchen sink? Because, none of the things you're talking about here address my point or they bring into so many other questionable things as to just be chaff.The benefit is being able to decipher the ritual in the Necronomicon that is going to save you and possibly the seaside village you are in... I'm not really a fan of mechanics that incentivize you to purposefully make bad things happen to your character. As far as control... isn't not being in control, relevant, etc the point of cosmic horror? And fun is relative, if you are buying into a horror game you are purposefully engaging with things that would otherwise be unfun. Some people would say no game where their character ultimately goes insane is fun and if put in said game regardless of the incentive would avoid it. You have to have buy in for horror period.
The Sanity mechanic in the DMG doesn't allow you to decipher the Necronomicon unless the GM allows it specifically -- it's not a tool in the hands of the player, it's another thing for which you ask permission. The main use for Sanity is a save replacement in the Madness rules. I haven't forgotten that you've explicitly made it clear that you do not use Sanity for how you're arguing here, but instead only as a save replacement. You were quite emphatic on this when I first asked you how Sanity might be used otherwise -- a position which you also, at that time, told me I couldn't ask about without allowing you to just say you used it as a save option for the Madness rule. So, yeah, the fact is that you're not even invested in the arguments you're making, it's just an exercise in internet arguing at this point -- you don't even use it as you're arguing it can be used.
The point about Cosmic Horror is about the genre, not the game mechanics. Otherwise, we can go to the extreme on that and say that no game mechanics are needed because there's no need for choice in Cosmic Horror, I'll just tell the players a story. This is obviously bogus, and so is the argument that the mechanic you do use shouldn't offer choices. The Cthulhu Dark ruleset offers lots of choice and still ends up driving hard into madness anyway. The fun there is to see how it happens. A Sanity mechanic shouldn't be punitive, causing players to avoid parts of the game whenever possible, it should reinforce and incentivize the play we want, which is the PCs sacrificing to try to stop the horrors from consuming what they love, even if it costs them their sanity. This is the play you want in Cosmic Horror, not PCs trying everything they can to avoid being hit with a hurt stick of the Sanity/Madness rules in the DMG. Those actively incentivize players to avoid anything to do with them.
For the preference you have to not incentivize PCs to do things that are harmful to them, I question this strongly. You clearly have no problem incentivizing players to go into dangerous situations and fight monsters at risk of life and limb. Given you use the Madness rules you clearly have no problem incentivizing players to get into situations where you can hit them with the Madness stick. Incentivizing players to do harmful things to themselves is an inescapable part of almost all RPGs -- the idea is that you are doing dangerous things that can kill you, maim you, hurt the things you love, cause you to go mad, end the world, etc. Yeah, this is something you absolutely do, you just don't like certain iterations of it where it's clear the player can gain a benefit for a harm within a single mechanic. Spread it out a bit -- if I spend some hitpoints and daily abilities and risk dying, I get loot and XP and the GM tells me more story stuff -- and it's just fine.
This bit is what I'm talking about with understanding incentives in games. You clearly haven't thought hard on the incentive structures present, because you've missed that you're heavily engaged in a strong incentive feedback loop already, but you're claiming you dislike such incentive loops.
Finally, the "fun is relative" argument is cliche. It's doesn't illuminate anything at all, and is an excuse to not examine play and see where it can be improved. Because someone has fun with a terrible subsystem doesn't mean that you can stop -- fun is had. It's very possible to improve that and get more fun, because fun isn't zero-sum. I might have fun in your game in spite of the Madness rules because I like playing with Bob across the table and we make our own fun and the killing monsters part of your game I really like. No, "fun is relative" is not a good argument, because even if we disagree on what's fun, there's always room to consider the mechanics and see if we can remove impediments to fun or add more. You cannot just assume that where you landed is where the fun is maximized or even good enough.