Why on earth would I even begin to look at my religion in terms of what is right for others? I must concentrate on MY service to G-d, not on how YOU relate to G-d, because I have a long way to go to conduct my life as G-d requires.
We all have our "instructions", whether it is through Christianity or Judaism. For a religion, or adherents of a religion, to consider that religion as "right" and the other as, therefore, "wrong" misplaces the emphasis of that religion.
So we are required to be the best Christian or best Jew that we can be as we strive improve our relationship with G-d. We should worry less about another's spiritual health and more about our own, because as our relationship with the Almighty improves, so we will have a profound influence on the spiritual health of those around us.
It isn't about right or wrong. It's about G-d and our relationship with Him.
Faith doesn't solely exist as some sort of abstract reality. It is a substance. It is evidence. If it is just "faith" in a completely subjective sense (no matter how much or in what fashion you attempt to remove objectivity from the equation), then it is useless. If my faith is in the Easter Bunny, I am not served by my faith. It makes me no better person. It leads me nowhere. That is because it is based upon a lie, a fraud. If there is no "things hoped for" or no "thing unseen" (to put it in Christian phraseology) then the faith is pointless. No matter what kind of warm fuzzies it gives me.