You judge whether they are good or bad by whether they have the same morals you do. If they hold the same morals, and exact them to a better degree than you do, you can usually find them better and therefore good(and likable). It also gives you something to work for(assuming that someone holding your morals, only better, would motivate you to reach the same so that they would bother looking at you). Either that, or they hold a different set of morals which you find better than your own, and are willing to switch to.
People immediately hating? Well, this can be caused by lots of things. Body language, asecclesiastes said something about, can reflect a person's morals. If you see that those morals are much lower than your own, or of a different, worse set of morals, you will be bound to hate them. Sometimes, it takes more than just sight, things like their manner of speaking, the way they talk, what they talk about(how they begin talking about something or how they continue to do so). If these show a reverse of your morals, then you are likely to hate them. These things may come off of gut feelings, but they are not.
Do we have a right to hate? You bet we do. A person of the correct morals has every right to hate those who have the wrong morals or who exact their own pathetically. You can hate-but you hate them in such a way that they notice it, but can still bear listening to you. Hate in that way will lead to a possible turn around-but if you hate them in such a way that they won't listen to you, they're not going to change to fit your views. Also, to do this, you better make sure your morals are the right ones. If they aren't, well, it's unjustified. No killing them for it.