Q: Is it ethical to conduct a study to prove something is good or bad, or right or wrong?
This is the domain of what is commonly referred to as “researcher bias.” When doing research it’s essential that you go in with a somewhat objective mindset. I say “somewhat” because we are always biased in some way.
Going into a study to prove that some trend is negative, however, sets you up for failure, unless you have a considerable amount of evidence from other researchers that you’re trying to confirm.
It works the other way, too: you don’t want to go in trying to promote something.
The middle path here is to pick a research problem that is complex enough that it doesn’t easily reduce to good/bad or right/wrong, open-ended enough that there is room for investigation, but specific enough that you can respond to it through a study.