This seems a very fatalistic and ego centered position. It is much akin to the notion that, I doubt that this child will have a good future and he is just going to die anyway, so I will kill him now.
In about 4 billion years our sun will go into a red giant phase, expand to earths orbit and incinerate the planet. If that does not get us a billion years later our Milky Way will collide with Andromeda. Not to worry though our sun is heating up, even as we speak, so in all probability our earth will be to hot for life in about 1 billion years. Also consider the increase in radiation. We must also consider that our moon is moving away from us and if it moves to far, we've got another problem, but, of course, that too, is a long way off. We also have the more mundane problems of meteorites and super volcanoes, like the one in Yellow Stone. Then we have us to consider and something called an atomic bomb, but all of our bombs cannot destroy the earth, but could have a really bad effect on life for awhile.
Also to consider those of us who wish to control the rest of us by whatever means possible. This can kill millions and return the Dark Ages.
Life has been on this planet for about 4 billion years. Our life form for about 250,000 years, homo sapiens-sapiens and I feel pretty good about us. I do not think there is any problem that we cannot fix, either caused by us or nature. We are very special, we can reason, ask a question and then provide an answer. I, personally, think that we should let that child live, as he may have the answer to our question. Admittedly we have answered a lot of questions wrong, but we are getting more and more right. Humanity is not me, it is us and we must survive.