"We can't preserve species over millions of years, so we might as well make them go extinct now" is not a good argument. It's like saying "we can't stop people from dying eventually, so it doesn't matter if I murder someone".

Even if you don't care much for animals, which is fine, you should still be worried about preserving biodiversity. We don't fully understand all the systems at play in an ecosystem, and killing some "useless" possum can have cascading effects that humans won't find favorable in the long run.

You can put a mine somewhere else, but you can't bring an extinct animal back to life.