Those are some of the things I've learned more about since I got into Kpop.
Now that Kpop is going global, Kpop agencies need to make a global history/culture awareness class for their idols before they debut. This way, both agencies and idols will learn more about what generally affects which people in different ways.
It's true that you can't please everyone but I'd rather someone gets criticism for something that doesn't deeply hurt an entire region like the West or East or a race or religion just because they are careless or ignorant. Kpop things should not mock other people's skin colour, religions, history and cultures.
On that note, Sowon should have known better especially when Gfriend promotes beyond Korea and Asia. And still, even if Nazism didn't affect Korea in any way, it's better to be empathetic to those affected or to just ignore everything Nazi to prevent hurting people.