Well, I don't consider Christianity to be a bare assertion in the same sense that if someone I knew made some claim without evidence that I had never heard before, and that I can't verify it for myself...I would just have to trust him. That kind of claim I could dismiss without much struggle.
With 2.2 billion Christians in the world and 1.6 Muslims, more care should be taken in considering the claims of these systems before making any conclusions. While an appeal to popularity should never suffice over actual evidence, it does give reason to use more care when considering a claim vs. a new claim made by an individual.
The bottom line though, is that I respect the right of each individual to come to their own conclusion, and to hold whatever beliefs they wish for whatever reason they choose. It would be wrong for me to tell anyone else what they must or even should believe. I might as well then go on to tell them what they must wear, or eat, or what kind of music they must listen to, i.e., to disregard their rights as an individual.
It is only when someone wishes to convince me of their beliefs, or states their beliefs as fact, that I require that they give me compelling evidence.