You equate possessing magic with being low borne but at the same time claim that even to possess it is a sin. How can one commit a sin simply by being? Does that mean you consider the poor child to have the sin of poverty? If he is an elf there is little he can do to rise above his station in life, no matter how hard he tries. And no matter how good a life a mage lives, he or she will never rise above being a mage. And therefore will always be marked a sinner.
Most of us learn quite early that life is unfair, Ser Alderic, I don't contest that at all. But there is always the possibility that things could one day change.
.... I suppose I sound rather like a heretic to you, don't I? I don't mean to get into such debates with a Templar, really. I apologize.