I can't get worked up about Mormons' baptizing my dead relatives by proxy. Do you want to know why? It's because I don't believe that Mormon baptism by proxy does anything. It signifies nothing. My dead relatives' eternal souls are unaffected.
Which is sillier? Believing in baptism by proxy or getting pissed about it even though you don't believe in it?
Besides, if the Mormons turn out to be right, our dead relatives will thank them.