Many genealogists have horror stories about family members who abused their access to a family tree they worked long and hard to grow. A relative who edits or distributes a family tree that another has worked on for years, without permission, is not being helpful.
It's painful for a family historian to discover that the information he collected, correlated and analyzed for years has been revised, published on the Web or even attributed to someone else.
While it might seem OK to make decisions about using a tree that charts our family's history, unless we performed the work, it's not acceptable. Even when we work with other relatives to create a family tree, it's best to consult with them about its use.
Although the worst offense is done by those who take credit for the work, the most damage probably is done by those who change a family tree. Some well-meaning relatives think they are improving a tree when they make the spelling of the family name uniform through the generations. What they may have done is curb the ability of future generations to find some ancestors in records because they don't know about an unorthodox spelling.
A family member might change a tree because he assumes that some people not on the tree should be there or vice versa. However, only blood relatives are traced in genealogy. The moment a genealogist starts to rely on records of step-relatives, they lose access to critical clues.
It's possible not to realize that certain marks or symbols on a tree are the family historian's way of indicating that some information is tentative. If a relative "cleans up" the family tree by removing "unimportant" notations and publishes it, they have virtually guaranteed that erroneous information will be passed on.
Never abuse the privilege of being allowed to read or copy a family tree. It's best to tell the family historian when you disagree with something. Maybe he will make changes or at least place a footnote on the tree. Future generations can determine what the truth most likely is for themselves.