I think the comments above about inadvertent changes to the tree reflect a short-term glitch in the system. That can't currently happen, unless someone has been invited as an editor, or unless you specifically choose to merge profiles from another tree into your own (and even then, it would not delete documents etc. that you have added, although it might overwrite dates you have recorded - also, it only would merge the immediate family of the person, such as parents, spouse and siblings, not a whole tree).

That said, however, some legitimate concerns remain - such as the one you have expressed.