Earlier quoted context omitted.
I'm in favor of privacy, and I'm willing to go more out of my way to not share than the vast majority of people, but I'm also in favor of individual choice, and I can't think of a privacy model that would disallow other people from sharing their information just because you have some matching information.
FYI, the police is able to find criminals now by finding DNA sequences similarities with your relatives. Not saying this is good or bad, I am just saying you don't know the extent of the impact to your personal freedom when your relative's DNA is shared.
And since 23andme (as I assume others) don't do these anonymously, there is no hope. Unless people use someone as a proxy (i.e. I-1 give my sample to a male colleague to send it as his-2, he-2 gives his sample to someone else to send it as his-3, and so on..). Police would eventually find the guilty in case of a crime, but the 23andme's of this world will be selling confusing (wrong) data.