Christianity Useful or True? A seeming contradiction.

More often than not, it would seem to me, people don’t discuss Christianity in terms of its truth or falsity as such. Rather, they seem to assume that the issue is one of merely social convention. That is to say, they seem to assume it false, but then want to debate its usefulness nevertheless. I doubt if they would consciously admit to that, but perhaps it is somehow assumed under the conscious surface as the starting point.
That would be an odd attitude, in my view. If Christianity is false, then “to hell” with its usefulness---who wants to live a lie? (maybe this is the point that escapes me however---maybe most people feel deep down that the best strategy is to convince themselves at some conscious level of the truth of a comforting and personally rewarding religion, and then ignore any arguments against it, at least at a conscious level). I believe we can detect a sort of “double standard” here, which reinforces my suspicion that Christianity is not really as fully believed as would be expected based on church attendance or church affiliation. This particular religion involves the promise and the belief that this world is somehow, in some sense, fallen, and that a much better world (“Heaven”) potentially awaits those who qualify it (what exactly “qualify” means here is a topic that we must defer, because interpretations of Christianity by the various sects, denominations, and theologians, differ greatly---some argue that only a tiny fraction of humanity will go on to this greater reality, while at the other end, some argue that all will be “saved”, and enjoy a wonderful, everlasting, paradise.). But, in my experience, Christians still seem to mourn and grieve over the death of loved ones and friends, as if their death is a horrible thing. If they truly believed they had escaped this earthly quagmire of moral decay, and were enjoying infinite bliss at home with God, then they would rejoice (though perhaps still allowing some sadness because they missed the departed, much as an inmate of a concentration camp might view the escape his friend into freedom. He would miss the companionship of his friend, but would rejoice that at least he was now free).