Anakin initially had some predispositions towards the Dark Side, perhaps after losing his mother, or perhaps he had some psychological issues (?)... But the fact remains: if Anakin had been unconscious, and Obi-Wan was fighting Dooku, I am 100% sure that Obi-Wan would have spared him... And if he had spared him, he would have likely told the truth about Palpatine.
Regarding the facts... this is quite doubtful... If Dooku had fought Obi-Wan, Obi-Wan would have most likely died, because he was one of the main threats to Anakin's transition to the Dark Side...
But in the end, it turned out to be much more beneficial to sacrifice his apprentice, Dooku... Because Dooku already knew many of Palpatine's secrets and could have used his newfound power to expose, overthrow, and kill Palpatine in time...
P.S.: maybe we should rename the topic to general philosophical discussions about choosing between Light and Darkness:D