does legality of a thing prevent big pharma from doing the thing?

This law is unrelated to big pharma, but I think the answer is “yes, but pharma follows the law.”

Or at least the law as they interpret it. Look at the opioid madness and even with that, I think big pharma was being Lawful Evil. Once the law is determined, I think they follow it. Even though they lobby to change it.

Big pharma does not run insurance

Insurance companies could directly ask for DNA if they don't care about legality. And in return they could easily offer say 90% discount to 90% of the people.

You actually do not need to ask the insurred ones. You need a family member that is with another insurrance company and conclude from there?

All I am saying is insurance companies could ask and people will happily give their DNA for say 90% discount(which I think they could easily provide). They don't need family members or any other things or any other backdoor.

Pharma is not insurance.

It was illegal in the movie Gattaca too, but they explained it by suggesting companies / insurance will just invisibly discriminate anyway which I think is most likely where this will end up in the real world