Should you tell someone that their religion is wrong? Only if you have too much spare time
It is very hard for me to believe that anyone is going to suffer psychological trauma from being told that one of the pillars of their faith is demonstratably false. If a person is so tightly connected to their faith that any threat to it will damage their psyche, they'll simply come up with some way to discredit you. If they can manage to shift their beliefs somewhat, then they'll find a way to incorporate your relevation into their existing belief structure. The extent of the shift they make will be a product of the degree to which your revelation undermines the basis of their belief system and their own flexibility.
I am amazed that so many people in this node really believe that they can seriously challenge the fundamental beliefs of other people. People who are really invested in something will stick to it, no matter what--and certainly won't be influenced by you. People who are less invested in a particular element of their faith won't have their minds blown.
Think about what would happen if archaelogists were able to demonstrate that they'd found the body of Jesus. Fundamentalists would just say that the whole thing is a fake. Liberal Christians would explain that the Christian message was relevant even though it had no factual basis (Rudolf Bultmann put forth a Christian theology that interpreted the resurrection as a metaphor nearly 100 years ago). A lot of people would just give up on religion; a few (myself included) would go to the nearest Conservative synagogue to offer an apology and get circumcized. Nobody is going to collapse in a heap of ruined belief.
There are a number of growing religions that have obvious factual errors (for example, a single course on textual analysis of Scripture will teach you enough to be able to identify the Book of Mormon as a product of the 19th century). I can explain this to Mormons until I'm blue in the face and it isn't going to sway anyone who wasn't already on their way out.
Is this news to anyone? I thought it would all be obvious.