From my understanding, most of what's inside our bodies isn't part of our genetics. For example there's lots and lots of bacteria, microbes, whatever that constitutes the fauna of the digestive system, it's not produced by the body but is essential to its functioning.
Once again, I don't really know what I'm talking about
We don’t even know the mechanism of action of many commonly prescribed drugs with certainty. We can’t cure rheumatoid arthritis or many other autoimmune diseases. Humanity is far indeed from from a universal vaccine.
Scientists don't have that precise knowledge of what the human body is made of. There is a whole microbriome of non human organisms that are vital to our health.
2) Even if we did, it would still be a major accomplishment to find something that kills everything else but not us. We are happy when we find a treatment that kills 1 bad thing without killing us.
3) The only mechanism we have for artificial immunity is vaccines. These do not kill anything; they just train our immune system. Given how our immune system works, this limits us to a blacklist approach, of training it to attack specific proteins.