I'll go with bad, not only because I think the Deathnote gives a person like Light too much power which can ultimately corrupt them, but because I'm personally against killing any human being even if they've done a terrible crime. Even if the majority of evidence can support a person had done the crime in question, there's always a chance, if only a slim one, that the individual is innocent of the crime.
I'll go into more detail about my thoughts on this, as I'm a fan of this anime and I'm against the death penalty, as that's what Light is basically giving to anyone's names he writes in his deathnote. Ultimately, Light believed that a presence of a God of sorts in people's lives would've kept humanity's tendancy to sin or commit crime in check, especially if that being had the ability to kill any who did wrong. However, it is unfortunately part of the human condition to sin and do bad things occasionally, no matter what forces tell them not too, even if death is the punishment for their sins. People sin or kill for basically three reasons - profit, passion, and compulsion. Those who do it for profit do it very rationally, beliving they'll never be caught, such as gangsters and professional assassins. Then there's passion, as if you're that angry at someone or something that you'd do something terrible to whatever is in question, then nothing not even punishment by death can deter you because thinking rationally can't usually overcome such a level of anger, such as finding your brother in bed in your wife and you kill them both in a fit of rage. And finally, compulsion, in which there is no reason for why the sinner commits the crime in question, because they did it on compulsion to get some kind of satisfaction out of it, such as serial killers. Granted, the presence of some kind of force that would punish criminals with death can probably deter them from commiting crime to a certain degree, but you can't fight instinct, and humanity itself has a very unfortunate complex balance of it's instincts of self-preservation and self-destruction.
As for the criminal in question being possibly innoncent when proven guilty by court or by the feelings of the general public, there have been several instances where people have been convicted of terrible crimes and later discovered that they were innoncent. This is due to that there is always a chance some kind of evidence, no matter when or if it ever comes in, or how weak or strong it is, that it can show proof that the person in question is innoncent of commiting a crime. And there's always the chance a witness to the crime or sin in question can mistakenly indentify a person for the one that did commit the crime, or even lie to protect whoever commited the sin if they happen to know who the person is. Even various prosecutors have been caught from time to time withholding evidence that the person they're trying to convict is innocent. You just can't kill somebody over something, because they'll always might be something that may prove of their innocence, and Light is basically giving into his temptations of wanting to rid evil in the most dumb way possible. Also, many also think killing someone in order to prevent others from possibly following their footsteps or teachings or even think of doing so, can possibly believe that, but if you do, then you should look towards several historical people like Jesus or Guy Fawkes that prove there are inspirational people who have been killed and who's beliefs still resonate in the hearts of many people who admirred or worshiped them.
As for Light himself, I once read a book that discussed about Deathnote and Light, that there are fans who believe and theroized that there's a possibility of Light doing what he's doing because he feels guilty over killing his first two victims with the deathnote. After realizing he killed two people with the deathnote, and his two victims crimes were the least serious of all the criminals he's killed, he obviously tried to rationalize to himself that they deserved to be killed and that all who commit crime derserve the same thing. He obviously knows deep down that he himself is a killer and by his logic, he himself his a terrible criminal who deserves to be put to death, regardless if he was doing whatever he was doing was for the benefit of mankind. But if it were up to me on how I'd punish Light for his crimes, I wouldn't kill him but I'd put him in some kind of Hannibal Lecter-like cell where he'd spend his entire life in, though Ryuk would of course kill him as he did in the final episode/manga of Deathnote when Light was found out that he was Kira. As far as I'm concerned, criminals should be kept in prison. If the prisons start getting overcrowed, make more prisons. If it's becoming more expensive, feed them cheaper food. Punishment doesn't always have to fit the crime, because if we have to try to be a better people, we must not submit to our sinful instincts, including the desire to get rid of those who threaten us or each other with a threat of death or misfortune.
In the words of Near in the final episode of Deathnote, Light is nothing more than a multiple serial killer with a god-complex, who posesses the most destructive murder weapon in history. Nothing more, nothing less.
I'll get off my soap box now.
