As far as I know they're completely unregulated in who they can sell your genetic info to, and they're pretty lazy in terms of information security. So maybe your siblings both send of their info to them, they identify that your family is at a high risk for heart disease, and suddenly your private health insurance company wants to double their fees. Or, with my tinfoil hat on, maybe your family is identified as being a particular ethnic minority, and an authoritarian government gets voted in in a couple of decades who uses that info to round up people they don't like. A bit far-fetched, but hopefully you get my point!