I got distracted before I could finish my post, I was going to say...
There has been so much harm done to the Irish and Northern Irish by the British and much of it within living memory, that just because I or my family weren't responsible for it, or because the Good Friday Agreement came into being when I was a small child, doesn't mean I'm going to judge those who still feel so strongly.
It's been less than a generation since the GFA and it will take more than one generation to heal the trauma and harm done to generations of people.
As another poster mentioned, the consequences of the history between the UK, the ROI and NI are still felt today and remain very relevant. Its a massive oversight that this isn't taught properly.
Unfortunately, its not uncommon to encounter racism against the Irish even now, the same racism that when I was younger and more innocent, I believed had died out before I was born. But then, I was also naive enough to believe anti-semitism ended when the Allies discovered the Nazi concentration camps(!)
The only Irish history I was taught at school was the anti-Irish racism that was rife in Britain in the c19th & c20th centuries - it was every bit as shocking as learning about the racism that led to the Nazis villifying the Jews & the resulting Holocaust. At some point I picked up on the so-called 'Irish Potato Famine'.
I'm not certain why the history isn't taught in British schools but I suspect the fact that's its both so recent and so raw is part of the reason.
(And also perhaps because my parents generation knew about it because it was part of their daily lives / news cycle. It never has been for my generation.)
The Germans didn't flinch from their Nazi history after WWII. If British people want to reach a point where hatred is no longer passed down the generations, then we need to ensure that the average person is educated far more about the history between our countries and the very real consequences still experienced today.
If younger generations on both sides can listen to each with an attitude of respectful listening, then we can start to heal the harm done, but we need to be willing to learn without knee-jerk emotional reactions.
You cannot compare the enmity that exists to the sibling-like relationship the UK has with France, that's ridiculous. And while yes, men returned home from WWII forever changed, that was a war entered into for very different reasons - and Germany has faced up to its history in a way Britain still hasn't.
We can't get upset or frustrated at anti-British sentiment because it's in the past when most don't know the history, otherwise we risk sounding like a certain type of American(!)
When we can acknowledge and teach our colonialism history properly that we can truly celebrate the things about us which we can be proud of.