The difference is that it is not yet fully understood how humans work. If you patch a machine and leave it alone, it will stay like that. Humans age, already

The difference is that it is not yet fully understood how humans work. If you patch a machine and leave it alone, it will stay like that. Humans age, already have or will get other kinds of diseases, have wildly varied genes, etc.. Drugs could have side effects not manifesting immediately, v2 of the same drug might have less of those side effects.