Since there is no concrete proof of anything relating to vampires, there is a lot of room for personal interpretation. That's where all the debate comes from.
Many feel that since it is something we are born with, you cannot force it on others if they don't have the predisposition for it already.
Other people argue that if you could find a way to damage another person's ability to maintain prana, either through draining them, psychically attacking them, or other methods, you could, in theory, "turn" them. Some claim to know how to do this, and other say they don't know how it is done but it is possible.
Still more people claim that you can use rituals to force out the human soul and replace it with a vampire's soul. The Aset Ka rituals are, of course, kept a mystery. You can, however, google "vampire spells" and find pages of magic spells that claim to have the ability to turn anyone into a vampire.
Then you get the confused and/or roleplaying individuals who say that vampirism is a viris that can be transmitted through sharing blood and other body fluids.
I'm sure that I'm even missing a few turning arguments, but these are the major ones. Now, who is right, and who is wrong? That is up for each individual to decide for him- or herself.