Well, it is not just the wet markets that is of concern. It is the commercial industrialization of the cow, pig, and poultry factories (...or meat industry in general). Consistently pumping antibiotics into these animals and keeping them in cramp, damp, inhumane conditions rapidly speeds up the pathogenic mutation process resulting in these super pathogens that are resistant and spill over into humans wrecking havoc. These pathogens have been here for hundreds of thousands of years but just only crossed over to humans hundreds of years ago due to the domestication and close quarter captivity of animals. So yeah, you're right, these pathogens are sort of man made; just not in some evil genius lab.

If civilizations built up natural immunity to thrive, then how was it the Europeans decimated the indigenous American population? How come none of the indigenous Americans ever gave any European their diseases? Why was it such a one way street? The theory is that the indigenous populations had very little diseases/plagues to begin with and the diseases that 'were always here' really wasn't the case. The diseases that 'were always here' really just came here hundreds of years ago when the Europeans first settled. Before the European, the indigenous populations had very little exposure to certain animals; for animals that were native to the land they had sort of a different relationship. Indigenous people hadn't really domesticated their animals to the extent the European had.
Domesticating cows and sheep led to measles. Smallpox came from camel pox. Domesticated pigs gave us whooping cough. Domesticated chicken gave us typhoid fever. Domesticated ducks resulted in influenza. Leprosy likely came from water buffalo. The common cold came from horses. When I say 'came from', I mean traced back to.

I don't think man were meat eaters from inception. According to the process of evolution, we evolved from apes (I think) and none of them are meat eaters. I believe they do eat bugs, but not other animals. If we were meant to eat meat, then we wouldn't have to cook it. Our digestive systems and teeth would naturally be designed to kill and eat raw flesh without getting sick. Just because man may have done something for thousands of years doesn't always mean to keep doing it. We get to live longer 'cause we cut out the dumb shit. Hopefully as we continue to find more dumb shit, we cut it out as well.