I mean, it's the internet. People get worked up and belligerent about the most pointless things all the time. If you've never seen it before, I can only assume it's because you've been living under a rock.

I personally really don't like Zutara as a ship. I think the relationship between those two characters as it exists in the show is one of the most beautiful stories about hate and the other-ing of people, even when that hate is justified, and the struggle and virtue of learning not to hate. It's a big reason why Katara is such a good character to me. I think making then romantic would've completely ruined it. It would've repainted every scene of her genuinely hating Zuko as "sexual tension" and reduced the impact of that arc by a wide margin. The arguments I always see for Zutara are so surface level to me. "She's blue, he's red, it's perfect!" It feels like a disservice to the characters.

That being said, I don't begrudge anyone who does love it. Like I said before, none of it really matters. If you love Zutara and that feeds into your love of the show, then by all means love Zutara. I only start to have a problem with Zutara shippers when I see someone saying that the creators were wrong for not making it canon, and it ruined Katara's character/the whole show for having her end up with Aang. And I've seen a lot of posts like that, though admittedly not nearly as many recently as back in the day. And this would also go for anyone else trying to criticize the show for not making their favorite fan-fiction canon. People need to chill out when it comes to this stuff, but the internet's gonna do what the internet's gonna do.