You know, discussing Mother Theresa is a non-sequitur anyway. A belief making a particular person want to give, or to take, or whatever, is not making that belief
TRUE.
If belief in Santa actually made children behave, wouldn't make Santa true. Maybe it makes it a useful lie, but it's irrelevant to its being true. Belief in the Tooth Fairy may make some kids behave when you take them to the dentist, but that doesn't make the Tooth Fairy true.
Or if, let's say, my giving to charity was actually motivated by being a missionary of Seven Dwarf Adventism (we believe that the holy Snow White is our saviour: she choked on the apple and died for our sins, and then rose again, according to the Brothers Grimm scripture

), or if I were even to start a charity in our
pale messiah's name, that wouldn't make it the one true religion. A useful lie to get some good done, maybe, but it's fully irrelevant to its being true.