In western society, "faith" and "religion" are nearly synonymous. Faith is necessary if the religion is based on the existence of another dimension that cannot possibly be proved, and that's by definition. Some religions seem to consider faith to be the essential ingredient, and anyone who does not have faith is not religious. More humanistic religions, and anything based on science, do not require faith.
We, in fact, consider the call to faith to be a scam.
If we go shopping for a new car, and we start asking questions about one in particular, and if the salesperson doesn't answer, but instead, says that if we believe that it's a good car, we'll be happy with it, what should we think? We should rather know that it's a bad car, or the salesperson would not have resorted to such obtuse tactics.
It is certainly true that we will never know everything, and we take many things on faith in this world. But whether or not to grant the benefit of the doubt is a decision that can only be made by the listener, on the basis of the value already demonstrated. Any call to faith on the part of the speaker is to be taken as an indication of the size of the problem that the speaker is attempting to hide. Any religion that is pure faith is pure hogwash.