Yue Zhong was forced to kill those infected 40,000 humans. If there were just one or 2, he might try to utilize surgery to extract the spawn out, and save the hosts' lives.
However, with such a number, he had no way of helping them. Furthermore, he wanted to bring them back to Earth. The moment one infected host got past, the entire China would be in danger.
Just one single alien spawn would evolve into a new Queen if it migrated to a place without any of its kind. It would then grow to become the single propagator of the alien species, and if left to evolve, it would only be a matter of time before it destroyed Earth.
After wiping out those hosts, the remaining 120,000 human survivors quickly embarked the Protector Battleships.
While every single Battleship was packed with the survivors, they were still able to ferry all 120,000 survivors.
