There's no need to care about their opinions, but what's being talked about here is not opinion. They're basic principles of color theory that have remain unchanged for centuries if not millennia. They became principles because they work. What do you think is more likely to be incorrect -- the millennia old principles, or your unsubstantiated, untrained opinion?

I agree with your chagrin for vanishing scrollbars and hamburger menus, by the way. There ought to be a good term for designers who do the opposite of what good design does (which is make things which are usable).