Mostly for one reason alone. Genetic association testing.
To get statistical power necessary to associate variants with complex genetic traits, we need very large sample sizes (hundreds of thousands are good, millions of individuals are better).
If everyone clings to their genomes in fear of what bad-actors might discover, we will never discover anything at all. Cures included.
DNA analysis of your microbiota can indicate more than just what you are or who you are, but also your current health status, where you have been, and who you associate with. It would also be one way to distinguish between identical twins.
When this technology is available, attackers will be able to perform biological exploits targeting individuals, families, ethnic groups or entire species.
Many examples are given of some conditions that are controlled by genetics and why an attacker would want to deploy them. Animal right activists making everybody allergic to meat, radical islamists rendering women unable to expose their skin to sunlight, a state ruining an enemy by inducing learning disabilities in children, an activist embarrassing his political opponent by giving him a fishy smell, etc.
Attacks can be immediate, delayed like a time bomb or even target the germ line.
One recurring recommendation is to keep your genome secret unless you have a medical reason.
Besides, the same knowledge that makes attacks possible also makes defense possible.
The best defense to the current threat landscape (privacy violations related to insurance, employment, and the law) is to define your genome-related queries as narrowly as possible and type/sequence only those relevant loci/regions.
The talk is absolutely amazing, probably the most captivating talk I have ever watched (thanks HN commenter that shared it a while ago). But anyway, Sotos specifically tells his audience that, as a security measure, they shouldn't release their dna to heritage services. Because it isn't vital.
Anywhi, great talk, highly recommand it although Sotos mentions DNA testing for heritage for a few seconds only, so slightly off topic :)
[0] https://www.youtube.com/watch?v=HKQDSgBHPfY