Are academic ethics global or local?
Your ethics vs the ethics of your community

It may well be that your personal ethics differs from the dominant ethics of the society where you happen to live, the society which is also setting the rules that influence your research.

While for many cases there's more or less a worldwide consensus about what's acceptable and not, there are genuine debates where multiple options are plausible, and in the case of such debates it's feasible that the IRB's of different countries would have contrary opinions.  One such factor where it's obvious why there are differences (and also obvious why some people may not consider the other's arguments as binding or even relevant) is religious influence which has some impact on medical experiments (e.g. stem cell debate or certain aspects of sexuality in some parts of the world), other factors of medicine include things such as research on certain recreational substances and euthanasia. There are also topics (or findings of fact) that are highly unpopular for political reasons, which again are local.

It may well be that the IRB considers a particular type of research unethical and unacceptable (i.e. it wouldn't be minor adjustments to do that thing properly but "your goal is taboo"), it's not a fluke and every IRB around them would consider it unethical, but the researcher, taking all the arguments provided by the IRB into account, still finds that they personally believe this action to be ethical. In such situations, a reasonably valid option would be to move to a location where the locally dominant ethics matches your own - and which would likely not have objections to that research.