some viruses have trouble living outside of animals (that is why smallpox was nearly eradicated since it could not infect anyone). there are ways to keep viruses alive in a lab. evidence that viruses cause disease? well, i will grant you that germ theory is still a theory in that it can still be tested, but there are studies whereby volunteers have placed rhinovirus into their noses, and guess what, they got a cold! surgeons use sterile technique and infection rates are incredibly low. people have been stuck with hiv contaminated needles and subsequently developed hiv. who knows where viruses first came from- are they damaged bacteria or single celled organisms that can't function without using another hosts cellular machinery? it is not clear, but many of them are very effective at what they do. i will continue to wash my hands and practice good hygiene. flu is very effective in that it can mutate and jump species; this has to do with it being an rna virus that is made up of various segments. what kind of proof do you need that viruses cause disease? you are making an error in attributing human characteristics to a virus. the virus does not think- it attaches to a receptor on a cell, or is engulfed by the immune system. once inside, it does what it does, takes over the cellular machinery and starts to reproduce. if the immune system or antiviral medication kills it, it does not lament, nor do its friends hold a funeral. it is just over. these are bits of genetic material, not upper food chain organisms.