There's a lot wrong here, so I'm not sure where to start.
First is the blanket assumption based on where someone comes from, which is a pretty low form of thinking.
Second, we don't know if Carlos Martinez has the virus.
We just know he has not been on the field. If he does have the virus, which he don't know if he does, what if he got it on the plane the league provided to get him and some of his teammates back to America? Is that being a loose cannon? Getting on a plane? Come on.
Is Harrison Bader a loose cannon for attending a party?
Carlos was competing with Kim for the fifth spot in the rotation because he has not had the physical health the past two seasons to stick in the rotation. He still has to meet that mark if the Cardinals insist on going with a five-man rotation. Unfortunately, he's at a disadvantage due to this delay that's keeping him off the field. Unless you have details about why he's delayed that I don't, and feel free to share them, the loose cannon stuff can take a hike.