He hated him and said he is disgusting kid even before killing his brother, so he hates him for his belief that he WILL do something, even without an evidence, which is for me understandable, because he would have really fixed things if he was a good king so sowoon wouldn't kill him..... about yona, sowoon loved her, and when he saw her he hid her from soliders, even was so sad when he saw her hair, so i don't think he is that he is that kind of eveil.
We are moving in a circle, so let's stand one the same land: if you are a practical person who values the country over a person, then you are forced to choose one, you will.. Does that mean that you wanted to? Or that you are bad to start with?.. no.
however, if the king wanted him to just whatever happen choose yona, then he is not even suitable to be a king, even if he is a good father and believer.
On the same idea, if we went far: the king does hate him even BEFORE he did think of ANYTHING, since he was born, just because he think that KID will do something someday!!, don't you think he got a role also in making the child sowoon be the person who he is that think less of god's believers who do nothing related to reality? In other words: effected his decision!
Well, anyway, I don't think anyone of them is evil, but sowoon is not hak.
We're going on a circle because you're not getting the prophecy. Nobody has said that he wasn't being practical or that he's evil, you're just assuming that.
The prophecy never stated Sowoon's reason to discard her, it just said that he was going to discard her, that's why Yona's mom told Hak to stay with her no matter what, and King Il entrusted her to him because he knew he was gonna die, and Yona would be in danger somehow. King Il wasn't assuming just to assume, his wife prophesied all that was going to happen in the future. Did you miss that whole section?
The prophecy became true at the end of the day.
If we're looking for the one's who started all this mess, it was Sowoon's dad. Just like his mother was explaining in her diary, her ignorance and prejudice caused a purge, in a way, it makes sense that the gods would punish them for what they caused, and Sowoon now has to deal with the consequences of his parents wrongdoings. King Il is not clean of blame, but he's not the start of the problem.
I am not mixing things, you said he ordered to kill her and that her father was right, but If we don't mix things like:
him separating things as a "practical plan" in normal situation,
and her witnessing something she can't see in this,
the problem is done.
He didn't order that because she was the king's daughter. And he never said I will absolutely never hurt yona. Which by the way what he had been resenting from all the time.
I know, and You can't do that.. It's called Self-investigation prophecy or النبوءة ذاتية التحقيق if the english version is not accurate, but search for it. I respect his beliefs, but even if they were real, it was made by his hand. he could behave alot better so things be different. Remember we are talking about a child that yet have done nothing.
I believe that sowoon's dad did right and wrong, but so is his mother who didn't speak up till the end. I don't really see anyone of them as an evil person.

Sowoon said he will separate boxes and his love for yona and revenge are not the same, which basically means he will treat yona will, then the king says he will discard her!! Where is the discarding I can't see it ╮( ̄▽ ̄)╭