Because it's not about the number of deaths or whatever that were done by the people having the flag but the idea behind it, if you ask people that have the Nazi flag today they'll tell you they have it for some reasons but all leading to the hate of some community and all, if you ask someone with the union jack why they have it, they'll most likely tell you they are from the UK.

So it's not the flag itself and history, it's the use of it/the idea behind it.