While thinking about this, Don't dismiss the positives of what we do. I read some excellent points on the minimal impact of aquariums on this thread. However, think about the positives as well.
1st, our hobby brings a love of nature for others to see. When we hear about some ecosystem in danger, we may process the information, but when we are able to see the beauty of the life in that ecosystem, it makes us appreciate conservation, not just for our sake, but for the sake of the life we have come to appreciate. Think about how a child lights up at the sight of a fish tank; think about how curious they become about what they are seeing. If I told you that a good percentage of the natural habituate of Live Breeding Endlers are being polluted, without knowing the beauty of these fish you may just dismiss it as trivial, but if you have seen how beautiful these fish are, this story may move your emotionally enough to act.
2nd, This hobby has had some negative effects in its history (growing pains), but today, our efforts (I'm sure) have probably kept certain species from being endangered or threatened. If a fish or plant that is appreciated in our hobby was/is having trouble in the wild, scientists don't have to figure out how to maintain a targeted species in an artificial environment because we (collectively) have already figured out how to do it.
Lastly, even though we are not perfect, what makes this hobby so special (to me), is it give us the instinct to love life, to love nature. That teaching (I'm sure) brings us morality. If our practices are less than perfect, but we care enough to try and improve on them because of the love the hobby brings. So, in my opinion, you wanting to care for plants & fish because you think it's beautiful, actually makes your more of a moral person, but this is just my thoughts/opinion.