Recognizing one human among seven billion by their DNA would probably take an unwieldy large amount of recognition sequence. Releasing a weapon with a killing payload and letting it be subject to natural selection risks it evolving to kill more people, or all people. In general, bioweapons are scary because they can't by their nature have reliable off switches.
They are also a heap of excessive effort when a sniper rifle or drone missile works fine.
They are also a heap of excessive effort when a sniper rifle or drone missile works fine.