I don't want humans to colonize other planets. Why? For centuries, eons even, there has been the age old fact of entire species being killed or endangered by none other than foreign diseases. The Bubonic Plague is one of those instances. Imagine what damage we could do to the wildlife of not only a different landmass, but an entirely different planet! And imagine what damage could be done to us. Our bodies wouldn't know how to react to foreign components and illnesses. It would require us to literally evolve an immunity to [planet name]'s different diseases. And what about the food? We couldn't eat that either. Maybe not even drink the water. On top of that, we would be starting from scratch. We would know little about wildlife, plant life, what's dangerous, what isn't, types of environments, natural disasters. But my biggest fear is: us. Even if we could triumph all these thing, the greedy and the soulless would just corrupt our new frontier all over again. Sell the animals as pets, crossbreed wildlife, genetically engineer them to fit OUR design, not nature's. We would drive MORE species to extinction because of hunting, a sport that would skyrocket with the discovery of alien wildlife.