What is the religious reasons against using CRISPR for strictly medical uses?

Whether it be CRISPR or some other gene editing technology, I have rarely seen any Christians think about the real medical benefits this technology could have for so many people. Instead, it is usually just brushed under the rug as not aligning with Christian teaching. My question is, why?

Say we could take an embryo and look at it using CRISPR to determine, and correct, if it displays signs of Down Syndrome, how is that against Christian teaching? If all you do is correct the genetic anomaly that results in Down Syndrome and take no further action to modify the embryo, I would argue you are simply doing nothing other than increasing the embryo's future quality of life. Isn't increasing the quality of one's life seen as a good thing? I have a cousin with Down Syndrome and I love him to death. They are one of the sweetest, most caring and most loving people I have ever and will ever meet. Reality is though, they will never be able to experience a life considered "normal" to the average person. They'll never be able to live on their own, attend college, have a family, etc. I wouldn't trade my cousin for anything but if I could simply take away their Down Syndrome and give them a chance to lead a more normal life, I would do it in a heartbeat.

I agree with and know of the many negative implications CRISPR could have and I personally believe it should not be privatized and its use should be strictly limited to real medical cases. It is by no means a flawless piece of technology, but if you limited it's use to strictly medical purposes and the treatment of negative genetic abnormalities/diseases, what is the religious argument against it?