Shipping neutral here. I don't mind either IR or IH, but what I'm trying to wrap my head around is why does Ichihime get so much hate? I don't see why people think Orihime is a stalker or obsessed when she does have a life outside of her love for Ichigo and shows concern for others, or that Ichigo 'doesn't notice her' when he clearly does and even comes to rely on her. I don't see how it's unhealthy or 'wrong'.
Its because for a long time people have been watching/reading bleach with a certain amount of tightly constrained shipping goggles.
A lot of people have been observing the series as nothing more than a weird coming of age romance between Ichigo and Rukia. Orihime to them is a third wheel that needed to learn her place (bow her head like a good girl and hop on her consolation prize which was either Ulquiorra or Uryuu depending on the era of Bleach fandom) and for that reason was hated when Kubo was showing signs he would go elsewhere with the character.
The soul society arc was huge which produced a lot of IR shippers. By the end of the arrancar arc they were still there even though IH began to form a much smaller but loyal following.
This inadvertently caused/influenced two things: a rise in the number of Orihime hate and the increase of toxicity within the fandom.
A lot of people seemed to project a lot of hate of her character based on their own insecurities or lived vicariously through Rukia and made Orihime the enemy for some reason. To them, Rukia was unbelievably strong, smart, funny, beautiful, snarky and tough who all the cool characters loved while Orihime was an awful big boobed whore who got in the way and people barely tolerated (including Ichigo). People would write essays about how unworthy Orihime was of Rukia’s friendship all the while writing headcanons of how much Orihime envied and secretly hated her and other female characters close to Ichigo. You can see this false dynamic play out in the way people write about the characters after the Bleach ending.
Anyway, Orihime has always been a perceived threat to certain pairing fans even when people tried (badly) to insist they didn’t see her as a threat. Any time Ichigo and Orihime had an interaction, there were several essays claiming they where unimportant. Anytime Orihime was shown to think of a nakama apart from Ichigo, people would praise her for ‘character growth’ but would go back to bashing her when Kubo stressed she still loved Ichigo.
They’d take any moment of Orihime feeling terrible as proof of Rukia being a goddess or the truth of IR. Take the notorious Orihime jealousy thing at the beginning of the arrancar arc. It was something that happened in one particular moment where Orihime couldn’t cheer Ichigo up because she herself had been injured alongside Tatsuki and Sado, which proceeded to reveal her own feelings of inadequacy that would be explored in the HM arc. Yet certain fans have twisted this scenario to make out Orihime is constantly jealous of Rukia (or knows the 'truth’ about IR) throughout the series.
Tl:dr Shipping goggles made people read what they wanted to in Bleach and blatantly misunderstood characters and their character arcs to justify their headcanons that were increasingly shown to bear little semblance to reality.
Take the last arcs of Bleach. People had noted dropped plot lines and the likelihood IchiHime was endgame but people still insisted Kubo ruined the manga for pairings that came out of nowhere (nevermind the dropped plotlines and character arcs which didn’t get resolution) instead of forcing Ichigo live in Soul Society with his 'twu luv’ Rukia.
Not to say others didn’t hate Orihime. She was a non-action person in a very action heavy manga.
But a huge amount of derision came from shippers who ignored where things were going after the SS arc.