Mold and bacteria and viruses are natural. Arsenic is natural. To strike back when struck is natural, but considered unchristian. Turning the other cheek when struck is considered Christian but it is unnatural. Monogamy is natural among some mammals, but unnatural for most mammals.
Reproduction is natural but marriage is unnatural.
Using condoms is unnatural. Dying of AIDS is to die of natural causes. Herpes is natural. Raping women is natural to some men, but it is usually regarded as evil nonetheless. In fact, ultimately everything which is made is comprised of nothing but natural atoms, molecules, elements, or substances.