There do seem to be some non-pathogenic DNA viruses, for example Foamy virus. Non-pathogenic viruses would be great to use for gene therapy applications, except DNA viruses incorporate themselves into the genome, which could drive oncogenesis. RNA viruses that are non-pathogenic would be great, but all RNA viruses seem to be especially pathogenic. Rabies, Ebola, Bas-Congo, Smallpox, etc.
Do there exist "gentle" RNA viruses?