Many see it as the day when "war" was declared in Northern Ireland; you can have your protest marches for civil rights but we are going to unleash unrestrained armed paratroopers on you. Can you imagine that happening anywhere else in the British isles?
Bloody horrible, and we never want to go back to those days. Bloody Sunday in 1972 escalated the troubles exponentially and IRA recruitment rocketed. Two years later came the Birmingham bombs and in 1984 the Hyde Park bomb.
Interesting point, but as we are seeing at the moment with the British border in Ireland the government seems to have selective amnesia about the GFA...