I fully agree with your apprehensions, but the question is whether this can be prevented at all. We shed DNA in useful, analyzable amounts wherever we go. In a

I fully agree with your apprehensions, but the question is whether this can be prevented at all. We shed DNA in useful, analyzable amounts wherever we go. In a decade or so, "collectors" of DNA from the air may sprout up everywhere, aggregating DNA of the passersby and sorting it into buckets using, say, face recognition. Even if such practice was limited to the airports, the databases will grow. People have to prove their identity when boarding flights, so pairing them with their DNA trace is feasible. And if a country bans this practice, another may not, and their database may be hacked and sold openly, so any person which traveled there will be exposed. The privacy argument might work in some Western countries, and the corresponding legislation may be enacted there, but once you have to travel to India or China or Dubai profesionally, the cat will be out of the bag.