The first things we hear about Slytherin in the series are negative. Voldemort having been one, Draco Malfoy aiming to end up there, and of course, Hagrid's ominous words. But no House is perfect, and Hagrid was a Gryffindor in his time, who was seriously and personally wronged by a Slytherin. It makes sense that he would view them as universally evil. However, when you step back and listen to the Sorting Hat from an unbiased perspective, it doesn't sound all that bad.
"Or perhaps in Slytherin
You'll make your real friends,
Those cunning folk use any means
To achieve their ends" (Rowling 118).There is no doubt that Salazar Slytherin was a nasty character, but that does not have to remain true for his House, centuries later. The traits that the Sorting Hat lists are cunning and resourcefulness, as well as determination. Those don't sound too bad, do they? It also implies that Slytherins keep the friends they make, and are very close to them. My real friendships have been close and long-lasting. It is not easy to drive Slytherins apart.
I can see why Slytherins have been the most likely to turn to evil. Often, their "ends" have been things that most humans long for, but are our worst desires: power and money, perhaps fame. But for a Slytherin whose goals in life are of a better, more moral nature, life is likely to go in a very good direction. Professor Slughorn's goals were selfish, but he led a comfortable life and helped many good witches and wizards on the way to fame and fortune. And let us not forget Severus Snape, who saved the world out of his love. Nothing could deter him from the job he had to do.
So what is it to be a Slytherin Serpent? Well, I think the best way to explain this is in an example of a situation that young Mr. Potter faced early in his days at Hogwarts: an enemy -- it does not matter who -- challenging one to a wizard duel.
"I'd take you anytime on my own," said Malfoy. "Tonight, if you want. Wizard's duel. Wands only -- no contact" (Rowling 153).I will explain what I think a student from each House would do here, based on the general qualities and qualifications for that House.
A Gryffindor, as we know, will accept the challenge, despite the danger it poses. Their courage and honor will not allow them to back down, even if they know nothing about magic or dueling. To refuse the challenge is to admit defeat, not just in the duel, but in the constant battle waged against the challenger.
A Hufflepuff will see no shame in refusing to fight. They are loyal to their House and to Hogwarts, and don't want to break any school rules. They especially don't want to lose House points for something as stupid as dueling another student over a petty disagreement, and in fact will find it honorable to refuse, because they are putting their House's needs above their own.
A Ravenclaw will think carefully about the challenge. They will likely know what a wizard's duel is, and have at least some idea of how to go about doing it. They will also be fully aware that a midnight duel is against Hogwarts rules, which they won't want to break. Depending on the individual, they will accept the challenge, not get caught, and win, or they won't care enough about such petty things as dueling ability when they have studying and homework to do. Maybe they'll propose another kind of contest, such as a chess game or a competition in Transfiguration (e.g. whoever can turn their plate into a teapot with the most success wins).
A Slytherin will weigh their options. They won't want to get into trouble and risk losing House points or marring their reputation. They will know their strengths and weaknesses, and therefore be aware of weather or not they could pull off something like this. In the likely event that they can't, being a first-year and all, they'll find some other way of thwarting their opponent. Either they'll offer a different challenge outright, refuse with a cutting comeback, or agree and lay a trap for their challenger. What Mr. Malfoy did was very effective, and though it didn't work, it cost him nothing in the end. All he had to do was tip off Filch that someone might be sneaking around the trophy room at midnight, and sit back as Harry Potter almost got caught. It really was very clever, and had Malfoy not been already established as an antagonist, we (the readers) might have truly appreciated it.
Being a Slytherin is not about being evil. It does not mean that you are immoral, or have selfish goals, or are prejudiced. It means that you are able to achieve what goals you set, and that you're willing to start again from a different angle when something goes wrong. It means that you aren't bound by silly rules about honor when you know that you can't win on strength or skill alone. It means that you can ask for help when you need it, and know when it's time to back down for a moment and think of something more effective. It means that you're willing to do what you must to get what you need, or to do what has to be done. Whether you take ethics into account is entirely up to you -- but I'm sure I'm not the only Slytherin who realizes that to harm others is to harm yourself, and that soul-ripping is definitely real and Dumbledore was right.
I am a Slytherin, because I think outside the box. I know where I want to go in life, and I work hard to get there. When something happens that deters me momentarily, I find a way to work around it or use it to get to a better place than before. I know how and when to ask for help, and it doesn't hurt my pride to do so. I am an extremely moral and ethical person, and I try my best not to be hateful towards anyone or anything. I can also see the impracticality of charging head-on against someone like Voldemort or a Death Eater. If I were at Hogwarts during the year when Snape and the Carrows were in charge, I too would have refused to do the evil things required of students, but my rebellion would have been quieter.
I do not discredit the hope that people like Neville were able to give with their outright resistance, but I would have preferred to offer hope without getting myself hurt or killed. In fact, it's likely that I would have started anonymously putting out pieces of writing that spoke against what was going on, and how the hate that was being spread was as destructive to the haters as the hated. I'd have made it a priority in the magical world to learn healing arts, and I'd therefore be able to help those who got hurt at the hands of the Carrows both emotionally and physically. I'd offer support of a quieter kind.
I probably would have wound up hiding with the rest of the DA eventually, because I would be tracked down at some point. Of course I'd be part of Dumbledore's Army. I respect Dumbledore very much, and being a Slytherin doesn't change that.
So don't despair if you're a Serpent. It doesn't mean you have to be evil, or are any worse of a person. You're in good company, if Severus Snape is anything to go by...
Rowling, J. K., and Mary GrandPré. Harry Potter and the Sorcerer's Stone. N.p.: n.p., n.d. Print.