Researchers come to your community and tell everybody they're studying genetic diseases. Their research will provide comfort to those who suffer. Sounds great, so you all hand over your DNA/ec to these researchers. Then a few years later, using that same data, researchers publish studies saying that your people are genetically stupid. That you're a bunch of subhumans generally unqualified for anything but menial labor. How does that make you feel the next time researchers come around asking for more data?
You'll tell them to fuck off, that's what you'd do. Why would you consent to research that demeans and degrades you and your people? And because your community now has an adversarial relationship with scientific research, that initial promise of research helping people goes out the window too.
If using this sort of data as a weapon against others is permitted, you harm not only the people you collected the data from, but your own ability to collect data from them again in the future.