I didn't hate him before, but after he's calling kaizer a monster twice i can't help it, maybe that's just normal reaction for a human like him but i can't help to hate his action (so it's just my personal opinion i think)... But from the comments, i think people also hate him for the fact that despite he's kind to tia, he actually had power to stop tia's abuse, but he didn't stop it because he didn't want to disappoint his mother,
Welp i posted my previous reply before i finish it, okay i'll continue... it's good that he already punished by kaizer and regretted that he let tia's abuse kept going, but it's just simply unforgivable i think, because tia got abused and starved for years not to mention she also almost got raped, any of that could be stopped by martin, but martin just didn't do it because of his mother (his mother is the one who's wrong, but martin is also wrong since he just have to be brave to fight his mother's will if he really pity tia)... After all that, now he suddenly wants to be a hero for tia, yes he just misunderstood the situation, but people might hate the way he kept taking the wrong action for tia both in the past and present time
I dont understand why everybody hate the knight...