In my opinion forcing a person to live when it isnt THEIR mind and body at risk is INCREDIBLY selfish. I can understand people worrying that a suicidal person is placing his bets unreasonably(about the chances of shit getting better) or thinking they are percieving the world in an unreasonably dark light, but regardless of what is wrong with their reasoning, it is the suicidal who will carry the burden of pain and despair if the white knight trying to convince them that the world is all sunshine and lolllipops is wrong.
Everybody has a sense of self preservation. Threat of pain, non-existance, hell, and the old question "what if?" all provide ample incentive to a person to not commit suicide. If suicide was easy, then the moment a person decided that chances were shit were gonna suck for far too long to make living worth it, they'd commit suicide without a second thought. There would be no moping, whining, cries for help, or talking with people about suicide, just boom, one thursday, dead.
Commiting suicide isn't easy. People who think that those commiting suicide are cowardly, weak, or quitters are applying THEIR perception of the world to a person who they know nothing about the inside of his head. That is short sighted, arrogant, and incompassionate. If someone does commit suicide, it takes every ounce of will they have left in the tattered disillusioned thing that is their soul.