>>12283017off-target effects from CRISPR-cas9 is a non-negligible possibility
you are STRONGLY underestimating how challenging it is to target repeats with CRISPR-cas9, or any gene editing mechanism for that matter. Targeting a repeat for editing is generally ill-advised and in terms of applicability to medical practice arguably would be foolish to pursue. let's take three possibilities: 1.CRISPR mediated treatment of late-stage HD: expensive, damage already done, no real QoL improvement. 2.CRISPR mediated treatment of early HD patient w/out significant neurodegeneration. Arguably best case for it but if off-target occurs (it's just a CAG repeat after all, not exactly a rare thing) you could fuck them up worse and QoL decreases (potentially). 3.Germline editing of parents concerned about passing along HTT to progeny. This is real nightmare stuff, because a germline edit would be persistent, their kid (F1) could have off-target effects not clinically presenting but then they have children of their own (F2) and some combination event results in a major issue in F2 generation (yes this nomenclature is typically for animals and no I don't care) which wasn't foreseeable. Major QoL impact, undue hardship, etc etc etc. All because of some geneticist with hubris, similar to the Chinese researcher that wanted to "cure" HIV by going against essentially consensus of the entire world. If even China wants to approach human genetics research/treatment ethically/cautiously, you know it's a big deal.
we would rather fix things with small molecule treatments i.e. druqs because if something goes wrong it's typically not permanent although that depends on half-life and other factors
There's a very, very promising metal-ion (Zn i think) small molecule treatment that targets HTT mRNA and prevents translation and is probably the best hope for HD treatment. Biochemists really are the best hope for the time being. Gene therapy isn't yet ripe for all but the most niche human applications.
