Yeah that's true, I was meaning that statement more for somebody that was an atheist/agnostic. You're right on that this is a weaker argument for Christianity, especially if you're talking about somebody that already believes in a different religion. If I were debating the merits of Christianity with somebody of a Muslim (or different religious) faith, I wouldn't even use this point, but would rather talk about the proof that is found for the truth found in the bible.
This kind of explains why I think of organized religions as "comfort blankets," because there aren't any real answers. Since I have a choice of either eternity after death, or nothingness, I like to appeal of eternity. But because every major faith basically says to believe a certain way (accept Christ, praise Muhammad, follow Moses), I can't figure why it needs to be just one of them. The basic moral principles are all the same, but by saying you need to worship and believe a semi-specific way seems like a scare tactic. I'd rather follow the ethics that religions share, than be spiteful towards those who don't believe as I do. From what I personally believe about God, he wouldn't judge someone solely on their specific belief as much as the merit their character holds.