I can easily imagine a reality where insurance companies have access (intentionally or accidentally) and give you a higher premium because they found something that makes you more predisposed to some ailment.

The above is pure speculation, but it's only one security breach or bag of money away. It's never safe to assume that a your data is 100% secure at a (presumably) benign company. As curious as I am regarding certain aspects of my heritage, the fact that I have no control over what they do with the info is keeping me on the bench.

The biggest risk of "sharing DNA" is pregnancy.

...I'll show myself out.

23andme already got hacked and 7 million people's private data was compromised:

https://www.theguardian.com/technology/2023/dec/05/23andme-hack-data-breach

The big real-world implication I'm aware of is that law enforcement can match DNA they found somewhere against 23andme's database. Then if you (or any of your relatives!) are in the database because they've ever used 23andme, they'll find that out, and they can use it to investigate or prosecute you.

Whether you think that's a good or a bad thing depends a lot on whether you think the cops should be able to succeed if they get a hold of someone's DNA and are looking for the person to match their sample against... that success is, to me, much more likely to be a good thing than a problem, but that may not be the consensus view here and it's certainly a massive, massive privacy implication.

https://www.dnasquirrel.com/ provides some guidance on how to get DNA results while maintaining privacy. I haven’t tried it yet, but I’d like to hear if anyone has.

If you’re like me, you could find out at age 38 who your true biological father is, and contact him for the first time. It may spiral you into an identity crisis, wondering if you should change your name and the name of your children. Here’s the thing though, my biological dad didn’t share his DNA. His first cousin did, and I contacted him.

As others have said, because you share your DNA with all of your relatives, it’s already not 100% private. One or more of your relatives has already tested their DNA. The most genetic privacy you can get would be for nobody to know who you’re related to. How tightly do you protect that information? Changing your name would be a good first step.

Your clone escapes, hunts you down, kills you, fucks your wife, and replaces you

You can call me paranoid, but the first thing I thought of when I heard about it was how excited the Nazis would have been to access a database like that when they came into power. Imagine knowing the names and addresses of whatever Undesirables you wanted to single out, and exactly what percentage of "impure" they were. Ethnic makeup information can also be used against you in things like gerrymandering congressional districts to hand select voters and disenfranchise minorities. It's pretty safe to assume that once your genetic profile has been gathered by a private company, it's vulnerable to all sorts of bad actors gaining access and using that information. Would you want the KKK or the Proud Boys knowing just what percentage black you are? No thanks.