@AlGarone Lmao, but really there is no conceivable answer why would someone hate him. He's basically like Janne, the newborn male version. He gets the chance to live normally, which would normally be impossible for a homunculus, but he still ends up sacrificing that for everyone else.
However as unfathomable as it may seem to be, a lot of people seem to have similar opinions and I have an idea why. He stole their pure waifu 😂
The hint came from F/GO where he and she are very hands off which is uncharacteristic of them. Obviously this was done to leave the self-importance of the player base intact. That's the most ridiculous thing ever, but it's true.
BTW, I recommend this manga as it seems to follow the LN closely. The anime changed some very significant stuff, like how Sieg and Janne meet.