Lupus: I got the idea for this while watching Markiplier play an online Would You Rather? game. One of the question was "Would you rather die a hero or live long enough to see yourself become the villain?" and for some reason I thought of Light Yagami. (I guess I'm just that much of a geek.)
Was what Light Yagami did good or evil? Light murdered hundreds of people, which was evil. On the other hand, he was doing it to save innocent people, which was good.
Killing people is wrong. That's the simplest answer one can give as to why Light was a bad person. Now let me point out that sometimes people are wrongly convicted of crimes. Sometimes they're framed, the evidence points to them for some reason, or they're just in the wrong place at the wrong time. Light killed so many people, he must've killed a lot of innocent people. Why would someone so smart not realize how many of those "criminals" could have been the innocent people he strives to protect? Furthermore, if those criminals were worth killing, wouldn't they have received the death penalty? Light barely took the level of their crimes into account. He saw that someone was a known criminal and killed them without a second thought. What if they only committed minor crimes and didn't deserve a heart attack? Light also didn't give people a chance to change, a chance to see the wrong in what they'd done. He didn't consider if they had families. Who knows how many people became widows and widowers and children became orphans because of Light Yagami?
On the bright side, crime went down. A lot. With Kira doling out his brand of justice, no one dared murder someone else or steal their possessions (though, in a way, this created a world of fear). This sounds like an ideal world to live in, right? A world where the people who really deserve to live can walk the streets without fear of dying. A world where less families are torn apart. Light saved more people than he killed. He wrote in the Death Note for a good cause. He just wanted to save people. Or did he?
Light wanted to be a god. He wanted power over people. He wanted anyone who opposed him to be in fear before he killed them. He was insane, arrogant, and creating a perfect world wasn't his only goal. He claimed to want to get rid of crime so innocent people could live, but it seems more like he just wanted to kill people until other people were in fear of him and he could rule over them. He was power hungry. Maybe at some point Light had the strong sense of justice people always talk about him having. But he lost it somewhere on his way to "Utopia". The Death Note changed something in him, but I'm not sure if it did it directly by possessing him or something or if knowing he had that kind of power made him go crazy. As is a lesson in many movies, power makes people go insane.
Going into Light's personality, Light was arrogant. I don't like Misa, but I also don't like that she gave her entire life to him, was willing to do anything for him, and loved him so much and he used her and pretended to love her for six years. What the heck, dude?! Light also liked to gloat over his victories. This was one of the things that brought his downfall in the Yellow Box Warehouse. He practically admit to everyone that he was Kira when he said "Well Near, it looks like I've won." He was so eager to taunt the stupid little marshmallow. Also, when he wrote down Naomi's name, he began taunting the dying woman. He was a total jerk. So it doesn't matter why he killed criminals. His personality itself was awful. And for someone so smart, Light was really stupid. What if Naomi had had a fake license with another alias? What if she had been walking away to tell someone that Light had just said "I'm Kira."? Why didn't he consider any of this? Plus he didn't even care when his own dad died and his sister got kidnapped. (Also, he got my poor panda killed.)
So I personally hate Light Yagami and think he was evil. But if you think about it, he might have been a little bit of both. I don't know. Everyone can have their own opinion about him.