I'm shocked to read that statement from that mum. I'm a bit disappointed and deflated but not too surprised to read from other posters here that agree with her.
I taught my dc from a young age when they started asking questions about life in general that some humans are good and some are bad, some are in the middle.
I taught them about colonisation and slavery but also about Arab, Spanish, America, other countries' war and fights, human rights' abuse even among themselves within their countries and continents too.
I taught them about the good and bad things happening in the world. I taught them that some people love or hate others for different reasons, it could be because you're rich or poor, loud or quiet, rude or too polite, a girl or boy, disabled or not, too nice or not nice enough, the colour of your skin, your hair colour, lightskin or darkskin, your nationality or ethnicity, etc. I never made 'race' the big bad wolf because I believe all hate is hate.
I taught them about many countries (including Britain) where people of the same race hate each other because they're of different religions or ethnicities or families or clans or tribes or social class. Some of these countries are at war right now and some are just casually abusing and killing each other left, right and center for being different (yet same "race"). Why would people hating others because they're of a different race or skin colour then be the worst thing ever?! Nope, not to me and thankfully, not to my dc.
Those who don't like us or treat us badly because of our skin colour or ethnicity are just as bad as those who don't like us or treat us badly because of a million other reasons. This includes people of the same race as us. We put them all in the same basket and treat them accordingly: ignore/ report/ respond where possible/ call the police/ block/ delete/ fight back/ defend yourself, etc. All depends on the situation and what it calls for.
We don't go about thinking all bad treatment is because of skin colour unless there's absolutely no other explanation. Even so, the abuser is the problem and not us. We don't give it any other thought besides take whatever action is needed. Yes we feel bad and comfort each other if we've been treated badly for any reason whatsoever, not just because of race. It would eat at our heart and self esteem if we did otherwise and cause unnecessary bitterness, resentment and anger towards innocent people because of the bad eggs among them. I wouldn't want decent people to do the same to me. I cba about the arseholes everywhere.
There are bad eggs in every group: rich or poor, man or woman, black, brown, white, middle class, upper class, working class, Cmhristian, muslim, vegan, etc.
Some people use the flag because they're racists. Some use it because they're proud of their country just like every other country and their flag. Some people are decent, some aren't. Not the end of the world.
FWIW, I'm black and so are my dc.