The show is written in such a a way where you can empathize with Uther because he is such a prominent character. but he is still... really, really bad! I keep thinking about this after seeing a tiktok comment saying he was "bad, but not like bad bad, just taken over by fear and hate" which annoyed me because that's how 'bad bad' people are created, they have weak wills and are overtaken by prejudice and selfishness and such. and also uther DROWNED CHILDREN! innocent ones who he suspected of having magic which was only a crime because he made nimueh make his mistake for him and then blamed her for it. Uther is a very very bad man. Again I can see where people are coming from when they say stuff like that (which isn't often, i do think that most of the fandom dislikes him, but there is a minority of people who don't think his actions are that bad (mostly people who i dont think pay attention to the show)) because hes such a central character, much more central than the sorcerers who attempt to kill him, who are justified imo.
Then with arthur like. I get why people like him. I like him. he's interesting and fun to watch and is the most central character in the shoe besides merlin. but people just constantly jump to his defense. again i havent watched the whole show so i'm going to wait to finish it to fully get a scope of his more antagonistic actions but... i dont think he really deserves the way that some people will totally just ride for him