Our Trees and the Mormons - Is there a privacy Issue?

Hi,

A distant cousin of mine raised a privacy issue about our trees and I would like to open up a discussion of the issue here.

Specifically, she claims that all (or almost all) family tree websites are run by the Mormons, who use the trees to perform proxy baptisms of our departed loved ones, thus making them members of the Mormon faith.

Is there any validity to this? Is this true for Geni.com specifically? Is there any way of knowing one way or the other for sure? If this is not the case, then how do I go about convincing my cousin?

Thanks in advance,
Mark