If a majority of citizens voted to legalize murder, would the government be right or wrong in doing so?

In most countries and most states, laws are not put before the people like that. There are a few states in the US where laws can be placed on the ballot, but a law like this would be struck down by the courts even if it did manage to pass. The US Constitution does not allow any individual to be deprived of life, liberty or property without due process, and allowing people to deprive others of the right to life without a trial would be blatantly unconstitutional.

ADD: The legal system in the United States does not really concern itself with morality OR majority. It is based on the rule of law. That means that the law is to be followed as written regardless of the polls and regardless of some group's definition of morality.

This is a tricky question to answer. Something you should know is that the founding fathers knew that issues like this would arise (Not this specifically). That is why they chose a representative democracy. That being said, they knew that the majority is not always right. They knew that the majority would be generally ignorant and emotional. Take 9/11 for example. The majority of the population wanted something to be done, and with their emotions taking control, the patriot act was passed. Most people would agree that would never happen now. It was because the majority was wrong; their emotions demanded illogical thinking.

The elected representatives act as a buffer to protect the people from the people. If the elected officials are aware that the majority only wants something to be done based on an emotional response, then they can do something to buffer it. The founding fathers hoped that the elected representatives were smarter and more educated than the 'every-man'.

Everything in the first two paragraphs should have answered your question, but I didn't do so directly. In order to avoid confusion, I will do so here.

Should they legalize it because the people have spoken?

No, major events often cause rushed and emotional thinking. The results of which can lead to things like the Patriot Act.

If so, is majority vote ever "wrong"?

Of course, the founding fathers knew this. This is part of the reason they chose a representative democracy. See above.

And if not, when is it acceptable to overrule the majority and when is it not?

It is acceptable to overrule the majority when it is necessary to protect the majority from itself. Like in the case you presented, murder; if this were to be legalized, then problems would obviously arise. Any educated politician would know that legal murder is detrimental to society.

The REPS are there to act using thier own best judgement. They are not there to simply do the bidding of the majority of their constituents. They don't hold referendums on every issue.

If the people they represent them aren't happy, they get voted out.

I take it you were dropped on your head as a child

they would be right

I THINK A MINORITY SHOULD BE SUSPENDED