Almost all the points covered.
-Failed attempts leaving you mutilated, blind, deaf, paralyzed, institutionalized, far more fucked than you ever were
-Failure could be seen as a lack of integrity Ie. foid style attention whoring
-Fear of and having to face regret when you've crossed the point of no return but have time to realize that
-Knowing you can't reverse the gunshot wound, you can't stop the bleeding, whatever poison is already on an unstoppable course through your body, you can't unjump off a great height, and you can't always free yourself hanging by the neck from a rope
Obviously if anyone has any lasting injuries they are going to regret it because nothing like that is going to equate to better anything and everything much worse.
One thing no one mentioned though is the forever lasting stigma you will get from just about anyone who knows you've tried to commit suicide. It's a another one of those taboo soyciety issues subject. Everyone is encouraging the 'talk to people about it' to try and fake normalize it. In reality you will still be looked at strangley, possibly bullied, ignored, or just treated oddly because of your attempt. It'll even have the ability to fuck you for certain jobs, licences (driver, guns, travelling abroad, etc.) This reason for regret is almost unavoidable unless you tried to kill yourself along, failed, didn't suffer any injuries, and no one knew.