first let me clarify that before i go into detail i am not an advocate for negative or unusual behavior. i just simply understand it.
"psychopaths, pedophiles, and whatnots, all those we consider bad"
most of the pain that people experience in their lives is inflicted by others due to a difference in opinion about right and wrong. to put it in a way that many might be able to understand - racism and homophobia.
if you were to leave a person who enjoys murdering/raping/pillaging/sleeping with children/whatever alone and just let them do what they want to do would they be happy? the answer is yes.
to say that someone who forces something onto another isnt happy in getting what they want is idiotic at best. if someone gave you a large sum of money with no strings attached for no reason would you be happy?
THE REASON why those who do things that society declares negative cannot enjoy themselves is because they have to suffer through mental agony in order to enjoy their lives in their own way. always hiding from the world because of a strange or unusual behavior.
for example cannibalism. to many humans the idea of our species being more than just another animal is actually due mostly in part to religion. in areas where religion was never developed (such as tribal islands) the humans that live there in tribes are only loyal to those they are allied to inside of their tribe - most of which is family. if you cannot speak their language and have a strange appearance you are a threat to their way of life and will be killed on sight if you provoke them. some are friendly. some are not. in the wild meat is meat and lazy overweight city dwellers and hyperactive athletes have a lot of meat.
whether you realize it or not many of our modern day morals and ethics have come from a few different places, but most are religion based or passed down from a previously successful civilization.
and in those times the victor wrote the rules. it's easier to convince an army to fight for you if you promise them safety and freedom. in order to have a larger army you have to protect your citizens from each other as well as invaders. any leader who would go against what they said after the war was won would be instantly killed off and replaced with a surviving member from the war that had nobility and was recognized as a major influence.
a single person is the weakest you can get. a family is a little bit stronger. a tribe is a bit bigger. a town. then a city. then a province. then a nation. and finally a continent. if you can convince everyone on a continent to agree to the same ideology and follow the same laws then your entire continent will be allied and anything or anyone that goes against it will suffer. humans do not like to suffer. so minor differences such as being gay for example if your allies consider that something evil or negative then guess what - you're going to suffer for something just because you have a difference of opinion.
witches were women and men who did not believe in a higher being, but instead in the practice of alchemy and an alternate plane of existence called the spirit plane. essentially alchemy was the base commoner version of chemistry. so literally for years people who wanted to advance medicine, technology, and science in general in order to understand the elements and how their universe worked were murdered for just being book nerds.
there are religions and cultures that when born into them you are forced to marry someone else. but what do you do if you end up not interested in them because you prefer a different gender? or a different species? some cultures have married their daughters to livestock to prevent curses from destroying their homes or to raise a drought.
pedophilia is something that has always existed. from the moment a girl/boy is born she/he is set eyes upon by any who would find her/him attractive or those who are sexually starved by not being "alpha" enough in their communities. in most communities it is the male who chooses the mate. royal families would lie about their children's ages and some wouldnt even keep track of their ages only concerning themselves with how beautiful or mature and well mannered they were. as soon as a girl had her first menstrual cycle she was considered an adult and married off to lords and bureaucrats sometimes in their mid 40's and 50's.
when given the choice most men and women would rather sleep/live with a partner that treats them the way they want to be treated, but remember women havent always had freedom to choose. and in those instances many many many things that we would consider unpleasant today were overlooked.
so to summarize -
negative behavior is defined by the majority because the majority usually wins wars for the king and the king makes rules in order to satisfy the majority so that the king will not be murdered after winning the war.
in most cases the majority want self preservation and freedom.
giving self-preservation and freedom at the same time is directly conflicting.
since self-preservation is the greater desired of the two any freedom that would infringe upon self-preservation of another is then deemed unacceptable.
unacceptable freedoms are punished.
those who do not agree with the limitation of freedom over the limitation of self-preservation (usually those who believe that the strong should feed upon the weak) are in turn forced to suffer for their difference of opinion.
we call these people radicalists. and for good reason.
now in turn if you have a majority that believes that the strong should feed upon the weak then you have something a bit different.