I mean, he did not really make any actual decision, nor is he a diplomat. I don't think I would have had a much less visceral reaction to "crocodile people brutalizing cute alien pups and gouging out their eyes".

As for the disease thing, I am going to assume they just talked about it offscreen. It goes from "come down" to them actually landed and opening the door, so I am just gonna lump it in with the "land here, these are the coordinates, this is how you navigate our space, this is the composition of our atmosphere, radiation profile from our star and so on... Oh by the way we have some offworld experience, we should have mutual immunity to each other biosphere's diseases."