Heritability of modifications.

Poor specificity and understanding of the consequences. Cure HIV and get some other genetic disorder (usually cancers) down the line because the sequence they used messed up other areas of your DNA.

Speaking more broadly, a genetic arms race to invent super-people. We already toyed with that once in the 40s, and it didn’t go particularly well. There’s a small technological gap between removing viral DNA for HIV and trying to insert or change DNA for unknown reasons. Cure illness? Great. Eugenics when we understand very little about the interconnectedness of our genomes? Playing with fire.

It’s fairly well understood. CRISPR cuts specific sequences of DNA out. If you’re too precise you won’t remove all the HIV. If you’re not precise enough you’ll cut out all kinds of other spots in the DNA and potentially cause problems down the line. A lot of experimental treatments like this wind up with patients developing leukemia or something else down the line. They state 12 weeks but it would be years before they can say this is safe.