I thought this one was... interesting. Certainly thought-provoking. However, I also think it was, ultimately, quite flawed.
Here's the problem: in order to make the narrator heroic, the author made everyone else an idiot.
The problem of the aliens was immediately apparent to me, even before I learned how fast they reproduce. Afterwards, the idea that everyone else wasn't asking themselves "where are we going to put these guys?" was laughable and distracting. I get that the story was all about the narrator being forced to make a terrible choice, but come on...
What makes this flaw so frustrating is that it would have been easy to solve. All it would have taken was a line or two of dialogue where one of the supporting characters gives some indication that this problem has been considered and that there is a solution in mind. The narrator then just has to chose not to believe in that solution.
However, I think that this flaw leads into the greater problem: this story was a moral cheat.
At the end of the story, the narrator has done something horrible. He's committed an act of genocide. The aliens he's murdered have - as far as we know - all intentions of sharing our planet peacefully to the benefit of all, and have no choice about going home.
In this day and age of entirely justified anti-imperialist sentiment, it's easy to forget that in the history of colonization, most colonies have consisted of people who had no choice about leaving and no home to come back to, like criminals, the desperately poor, and oppressed religious minorities. Most colonies have also included, say, innocent children. I'm not apologizing for colonialism and imperialism - what I'm saying is that the hard reality is that there are individual innocents and people with the best of intentions on both sides of these conflicts. Some day, let me tell you about how it sometimes seems to me, looking at our history, that America almost could have been a multiracial anglo/native state, with the two populations peacefully coexisting and gradually interbreeding, their cultures and religions gradually mixing.
Anyway, the narrator didn't care about the innocents, or the possibility that the aliens had no way to go home and no home to go back to - he made his choice and doomed all these people to die. It was important to the story that there be no solution to the problem - that all the other characters be idiots - because it made the moral situation more black and white (blacker and whiter?). With no alternative on the table, genocide becomes a lot more attractive, and the narrator's choice less repugnant. If there was a solution - and I maintain that it's foolish to think that there wouldn't be, even a flawed and complicated one - that the narrator chose not to believe, then the narrator's choice would have been a lot more complicated, and the story all the better for it, but he would have lost some of the readers' sympathy.