Well, for starters you're reducing the number of attack vectors. If the only animals we can eat are a small number of species from regulated farms, any crossov

Well, for starters you're reducing the number of attack vectors. If the only animals we can eat are a small number of species from regulated farms, any crossover/issue is contained and traceable to those species and farms. If you allow (including as a purchaser you create demand for it), in open market a wider range of species from a wider range of sources, you open up the number of attack vectors increasing risks to everybody on the planet.