Although it caught us by surprise and was heartwrenchingly tragic and sudden, I feel like it built well into the character development of Eggsy and how he went on to save the world. I thought the last 30 minutes of the movie wouldn’t have been as impactful if Harry had lived - his death set a precedent that anyone could have been killed off instead of following the “good guys who are beloved characters are all powerful and can live through anything” trope.
Also it’s rich grounding for the eventual PTSD fallout post-V-day that I have as headcannon for Merlin and Eggsy considering they witnessed in first person, Harry’s head snapping back from the force of the bullet and then smacking into the ground from the fall backwards.
I should also note that the main other fandom I am part of has had a leading good-guy character getting decapitated about 10% of the way into the story.(Who at that point in time is recognized as more or less the most powerful being in the series, and is universally adored by fans) Yes, the unshakable, all-powerful godlike angel of a leading character had her head cut clean off in front of the little kid she rescued from unfathomable abuse to whom she was the only living companion, caretaker, mother figure and protector. (Sound familiar? And you thought Harry’s death was bad!)This happened with no lead up or foreshadowing that something like this happening to that character was in the realm of possibility. And you better believe that overly tragic events like this makes for really amazing setup for character development of that little kid after.
I speculate that the sequel to Kingsman might go in a similar direction with regards to shaping Eggsy as a character (I trust this was what Matthew Vaughn meant about Kingsman being the prequel to Eggsy’s story) and I cannot wait to see what happens next. Even if I still really want Colin Firth to at least come back in the form of flashbacks. But I feel the integrity of the first film would be compromised if Harry’s all fine and dandy/100% a-okay in the second.