GoT has some real assholes, mostly because the conventionally good/honorable characters die quickly.
But Eurons troubles aren't his moral failings.
Euron Greyjoy in the books is a politically savvy viking warrior who kills his brother to become king, and makes alliances to benefit the Iron Islands (his kingdom).
Euron Greyjoy as written by D&D is an insane troll who fucks with people just because he can: his enemies, his allies, anyone.
Adding to that is the way the Iron Fleet under Euron Greyjoy is used to beat the 'good guys' no matter how smart or clever or powerful they are.>Yara and Theon bring some of the Iron Fleet to Danaerys' forces>Euron's fleet destroys that>Tyrion has Danaerys' Army take Casterly Rock, it's a trap (no gold, no food, empty fortress far from anywhere), good thing they have a fleet of ships they can sail away in. >Euron's fleet destroys that
Danaerys has dragons - giant firebreathing, flying lizards>Euron's fleet shoots one down with sniper ballistae after coming out of stealth mode, almost gets another one.
Show!Euron was just a flatter, more comically insane version of Book!Euron.
Then he became the writers plot-resolution tool, and people really started hating him. Which is a shame, because Pilou Asbæk (the actor) does an excellent job of playing a viking madlad.