I don't think they realized how screwed up their "aliens" still were, even on the 8th attempt.
The Queen seemed weird, and likely there may have been other problems with them, that we just did not see.
The Queen made no move to defend herself at all, and jut let the Newborn rip off her upper jaw.
I do agree that the Newborn is not good for the alien species, and that the mutant hive was doomed from the start.
In a way the newborn killing the Queen was the best thing it could have done for the purity of the alien species. They are genetic f**kups, so reproducing would only hurt them as a whole.