He uses the law in place of morality. His logic seems to be if it's the law it's right. The end. As though the laws weren't written by powerful men who wanted to stay powerful and were also flawed.
Ned also abides by laws, does that makes him a bad person? I don't see how following laws can be used against someone.
People often quote his line about not making human sacrifices in ADWD as proof that book Stannis would NEVER kill Shireen like in the show. But he allows Mel to burn his soldiers, relatives, enemies, etc. He could stop her any time. The burnings are his as much as hers.
Everyone Stannis has burned in the books is because if they have done something worthy of a death sentence, he doesn't do it to please Mel or on her orders.
He may yet burn Shireen in the books but it remains to be seen under what circumstances he does it.
He seems to have no respect for Jon's vows. He doesn't offer Jon legitimacy out of the goodness of his heart. He wants to use him and plays on his emotions in an attempt to twist his arm. He doesn't care that Jon swore a sacred vow to not be involved in such things. He treats Jon as though he owes him for beating the wildlings, which leads to 4.
Stannis isn't the only one who wants Jon to be the head of House Stark even Robb wanted to relieve him of his vows and I am not sure of it but I read somewhere that people have been relieved of the Night's Watch vows too.
He has the not very kingly attitude that he should be repaid for rescuing the Night's Watch. He demands his men be fed by men who will likely starve come winter because of it. And he tries to push Jon into giving up castles along the wall, something that, again, goes against Jon's vows.
He saved the Watch from certain death so I don't see any problem in demanding his men being fed, the castle part is wrong on Stannis' part.
He's so unlikable he has no followers of his own at this point. All his men are "queens men" who are cult members who like him because he burns humans.
He has hundreds of soldiers that are not the queen's men and the Mountain Clans are also in his support that he won over himself.
He tries to ruin other people's fun just cause he doesn't know how to have any himself. What kind of person tries to shut down brothels? Come on, man. If you can burn people let them fuck people.
People would do more productive work if their are less distractions.
He was an asshole about Gilly's sad upbringing. Remember the bit in ADWD where he calls her and her baby abominations because her dad was its dad? As though she had any say about being raped.
Stannis doesn't know she was raped, does he? He may very well think it was consensual. Or perhaps he was just a jerk in this part.
He locked Davos in the dungeons for weeks after Davos lost many of his sons in his battle and was stranded on a rock at sea for a painfully long time. Great friend.
Then made him his hand and raised him to lordship. He got angry that Davos betrayed him by plotting to kill Mel so he had him locked up.
He drives people away with human bbqs and being the emotional equivalent to a rock, then pouts and has a pity party about being unpopular. It's like a kid lighting the person at the desk next to them on fire, then whining, "why doesn't anybody like me?? I don't understand! It's so unfair! You're all assholes for not making me class president." lights teacher on fire.
Stannis was disliked even before he started burning peoples, the reason was him not being very social and comely. Stannis can't help these things so he feels whines about people disliking him.