Ethically we do things every day that shouldn't be done.
Driving causes pollution.
Flushing the toilet puts unknown hormones into water systems, some of this can find it's way back into rivers, oceans, lakes etc.
Advancement in medicine would not be where it is today if it weren't for the unfortunate sacrifices of testing on animals. (Although I do have an idea on how to avoid animal testing altogether)
Turning on your T.V., running your household, charging your cell phone, anything involved with the usage of electricity puts a drain on resources and leaves a carbon footprint.
Eating in general could be called unethical. Pure vegans don't eat meat of any type, but they do kill plants. Us omnivores eat everything, so we're killing plant and animal.
Filling our tanks puts a strain on fresh water supplies.
Cross breeding franken-fish like the blood parrot, breeding fish for certain deformities like the balloon mollies and rams.
Pretty much anything we as humans do can be considered unethical by at least 6 religions/beliefs that are based on nature instead of one omnipotent being.
So I'm sorry if someone thinks that by me having wild collected fish in my tanks is unethical, but I am giving those fish a fighting chance compared to what they would have in the wild with us bipedal apes running around ruining their natural habitat.