Why does everyone hate Tess so much?

Currently at the beginning of volume 7 - chapter 201. I had a few questions so I thought I would check he reddit but I just saw loads of people disliking Tessia especially in volume 7 and 8, I was just wondering why?

I also got spoiled quite a bit so I know that Celicia will use Tessia's body as vessel and I was just wondering if later on in the story if Tess is freed by Arthur?