Put me in coach, I'm ready!
Good questions! In fact, this is the topic of many panels regard colonizing other planetary bodies. Usually goes something like this: "Look, we goobered our own planet, what is to say we won't do it again?" That is a fair criticism, but here are a few things going in our favor. First, we have learned a lot about what is causing our planet harm that we may not have been aware of before. The whole "fool me twice" thing would be tougher to pull on us. Second, we are assuming the planet/atmospheric make up is similar to what it is here on Earth. We can also toy with the idea that an atmosphere that might be inhabitable will have different traits that make it more... resilient to our waste products. Third, our technology is rapidly expanding, in that I firmly believe that given enough time we can correct environmental issues and allow us to be more sustainable should we get a second go at another planet. There is more, but let's move on.
First, it is worth pointing out that as far as we know the moon has no natural resources that we can readily use. Sure, we can use it as a launching pad, but basic physics tells us that launching from the moon would not be efficient. At all. In fact, the greatest asset to our space travel is not an actual planet or moon, but gravity! We used gravity sling shots to get Voyager into position to get a selfie with Pluto! And it is STILL going! All from an Earth based launch, not too bad, eh? Second, there is a common belief that natural resources in space are as rare as they are here. We do not believe that is the case. When we begin to discuss things like hydrogen, ammonia, and oxygen; even minerals such as iron, gold and aluminum; we have reason to believe that asteroids and other planets will have very large amounts of these things. In short, we could be one asteroid away from having enough aluminum to last us for generations. In short, most elements are really common elsewhere, even if they are rare here. Something to think about.
Now, a key difference is that we, as humans, are self aware of our destructive nature. We have a conscious and a moral responsibility within us to do the right thing. That is not to say that we will do the right thing. But, I have a but more optimism that we will not turn into a galactic virus that destroys everything.
Our primary purpose for space travel right now is self preservation. Eventually, we will not be able to stay here. For better or worse, due to whatever circumstance, we will eventually have to leave or we will perish as a species. So, any data or technological test that can get us one step closer to that, we want. We want it as soon as possible.
I will take this time to say we have no moral obligation to the universe if we become extinct. Right? If we are all dead, we owe nothing to anyone because, well, we are dead. So, from my perspective, I welcome any and all technologies related to space and our ability to become multi-planetary because our survival comes first. Problems faced after we have established ourselves will happen and we will have to overcome those. But let's not put that cart before the horse.
Hope this helps.