If you started reading this article first, please go back and read Spellcraft and pay close attention to the part about not casting spells on other people without their permission!
A "hex" is a spell that is cast either on another person who has harmed someone, or on a situation that has harmed someone. Sometimes hexing the situation is preferable to naming names if you aren't positive you know the correct persons' identity. A hex is done on a person is without their permission, obviously, and so is considered imposing your will on another person, and therefore is unethical magick.
I do agree, however, that "A Witch that can't Kill can't Cure". There are times when a person feels that she has the right, and maybe even the duty, to get justice done in certain situations. I will not tell you that you can't do this, you can. I will simply warn you that this is not for the dabbler in magick to attempt, or for the first or second year solitary student to try. This is serious magick and can and will have serious repercussions on the person who performs it. Before doing any kind of hex you need to understand that part thoroughly.
I will not argue with those who believe that karma doesn't exist if you don't believe in it, and that they can do whatever they like magickally and not be held responsible for their actions. Wicca teaches us that we are responsible for all of our actions, and hexing is no exception.
When should you hex someone? Is it ever "right"? Is it okay to cast a hex on a child molester or rapist or murderer? I can't answer that for you, that is a question that only you can ponder and decide. I can however advise you to be sure to get ALL the facts before making your decision. I also advise that you don't name any names if you can help it.
If you have been wronged, and you are doing this hexing for yourself, then this can be considered self-defense, and the karmic repercussions could be beneficial to your life. See, this can get convoluted, can't it?
I have used a method which will bring about justice on the person, without naming names or incurring karmic nasties. This method is to tell the cosmos what it is that has happened to you, and to ask for justice to be done to the party or parties responsible for it. I will not give exact examples here, but if you read the articles on spell construction and what elements can be involved, and what different colors, days of the week, and so forth stand for, I think you can craft your own spell quite nicely. Also see "reversing negative magick" for a spell that will ethically bring about justice.
The most potent spells, the best spells, are the ones which we make for ourselves. In the case of a hexing spell, my belief is that it won't work well at all unless you make your own. Each individual case is so very different that the spell must be written exactly for the incident in question or it will lose it's effectiveness and may even cause harm to the person doing it. Hexing needs to be very precise and very specific to do the best job, so you really can't have an "all purpose hex" like you can for example for a money drawing or house blessing spell. Each one needs to be written for the specific situation.
There are certain questions to ask yourself:
If you can answer definitely yes to the questions above, then there probably is a need for you to do this hex. Before doing anything though, I advise you to speak with a trusted friend or teacher, someone's whose opinion counts to you, and ask them to advise you on the matter. Please don't ever decide to hex without speaking to an elder about it first!