Which TV character is so beloved in a fandom, you get attacked instantly if you share a critical opinion about them?

Dean Winchester

Spike, from Buffy the Vampire Slayer. On the Buffy sublistnook, you cannot say anything critical of him and his relationship with Buffy without being downvoted and argued into oblivion, it’s ridiculous.

Cousin Richie in the Bear. I don't believe that wearing a suit cured his ADHD and childhood trauma but those are fighting words apparently

Spencer Reid from Criminal Minds

Dr Robbie on the Pitt. Season 1, we all loved him but season 2 added a little more depth and complexity and in reality he’s just a stressed out boss in a highly stressful job. Wants everyone on their A game and is quick to judge and lash out when he too is dealing with heavy shit. Still a great character but a little harder to digest in season 2 compared to the other characters around him.

In no particular order: Ron Swanson, Bubbles, Paulie Walnuts, Creed Bratton, Charlie, Bonnie McMurray, Jason Mendoza, Boyd Crowder, Alphonse Elric, Mr Carson, Disco Stu. I’m sure there are plenty of others I can’t think of at the moment. Based on the parameters set by the OP, these would be characters who would be basically impossible to criticize.

Schmidt from New Girl

Walter from Breaking Bad, especially in regards to attacking Skylar.

I hated when it became apparent the direction George Martin was taking Jamie Lannister in. My opinion didn't improve with his portrayal in the show. Too many fans lauded him as a badass even though we never actually see much of his martial skill. He likely never killed anyone before Rory and then being unleashed against the unprepared Riverlands. Aerys knighted him young to spite Tywin and kept him close, then Robert kept him leashed to mock him. He himself couldn't come up with much besides tournament wins when he was feeling sorry for himself at his poor showing in the White Book. And regardless he was rendered useless before the end of the first book. Who cares what skill he might have had. As for his great deed and resentment of how Ned treated him, that was his own pride. There's not really any other way Ned could have viewed him sitting on the throne with the king laying dead and the city sacked by his father. Just tell people what happened. If he was really worried about the city, leaving a cache of wildfire buried beneath it wasn't wise. And the way his fans defend his attempted murder of Bran. The kid was playing in his attic, not spying or meddling. He likely didn't really know what was going on, could have been scared into staying quiet, anything but being killed. Then how his relationship was actually okay. Can't even get into that. Just a petulant rich boy.

For some reason, apparently Samira Mohan

Stiles from Teen Wolf

Elliot Stabler

Rick Sanchez

Rory of the Gilmore Girls

Iroh

I don’t think the Fonz was very cool.

Peggy from Mad Men (at the time)

Come for Elliot Alderson and you’re dead to me.

Shane and Negan from The walking dead.

I guess in the Gravity Falls sub, Pacifica for some reason?

Ilya Rozanov. Yeah he's s*** as shit but he has issues too

Christian Kane

Darryl Dixon

Zeke from Manifest.

Min Ho in xo kitty 

Apparently Wonderman

I thought part of the allure of that show was hate watching as almost every character on that show was more insufferable than the last. I don't really have a specific example in mind, but there's a somewhat related thing that really irks me. If you dislike a fictional character, such a common Listnook response is "Oh you must hate them because they're [___]". No, disliking Naomi from Expanse or Brian from Shrinking doesn't automatically make you a racist or a misogynist or a homophobe.

Rick and his kids on The Walking Dead

The Ross and Rachel relationship on Friends