Think of how bio-weapons and other means of debilitating were used in war, since time immemorable.

Catapulting diseased animal and human corpses over the walls of castles and fortifications being sieged so that the defenders have to contend with sickness. Dropping carcasses into wells, ponds and other water sources ahead of hostile forces. Weapons to wound rather than kill soldiers, so they become a resource drain on their squad who have to medic them, evac them, having their mobility ruined etc.

Sending diseased people to a place is an act of war against that place, and welcoming these people in knowing that you are expending scarce medical and hospital resources that are owned and needed by the host nation can easily be malicious as well. Altruism is only the excuse.