Well you will lose your humanity, sanity and go hollow if this happens too many times.

I'd rather give to a probably mighty warrior the chance to kick the ass of whatever corrupted my master rather than stopping him and waiting for the world to collapse.

Also what is Sif protecting,exactly? Bones?

Not really, who dragged the half rotten body of Artorias all the way from Oolacile to the Darkroot Garden?

Ciaran asks for his soul, but that's as far as it goes

It mentions in the sigil you buy from Andre to open the door that it's a dangerous item because it leads to an area crowded with bandits and thieves that looks for fortune but ends up dead.

It's literally just a grim forest with an old tomb, there is nothing valuable there, only a powerful ring that lets you travel in one of the most dangerous nightmares of the game to kill a boss, not exactly something you can sell on Ebay.

I know I'm overthinking this but just for conversation's sake.