I think this question resulted from me having an argument with my gf. We want to go to a holiday trip, and she wanted to book a hotel via booking.com. We then got into a discussion, because booking.com repeatedly ignored privacy concerns and is conciously acting illegally in regards to privacy laws of the EU (for those of you who can read German, this link from a German privacy investigator explains it fairly well. In my opinion, supporting companies which consciously breach laws is unethical, because they willingly ignore the well-being of their customers for own gains. However, in this case it was probably unfair to gf to judge her for using this platform, as the negative impact done by her using booking.com is not enough to justify this as a morally wrong action on her end.
My question is where you draw the line what to ethically judge. What if (hypothetically) booking.com would support slavery and willingly sacrificed children to earn more money for their shareholders? What if they were very interested in animal abuse and liked Nazis? In this case I think I'd be completely justified to judge my gf for her using this platform, as she would then directly support inhumane and unethical practices.
Most of life, however, resolves in a grey area between "this is absolutely morally okay" and "this is terrible, anyone who supports this is a monster". And so I think your opinions on the topic of an ethical line would be highly appreciated.