Your friend may say that sin and evil have always existed. If this is the case then he is saying that these things are equal to God in the sense that they have both existed forever, from everlasting to everlasting. If sin has always existed then the only conclusions left is that sin has always existed with God as a separate entity or that evil is a part of God's nature because He is the only one that has existed for all time. Both these conclusions are ridiculous as they suggest that God himself is either evil or that evil is equally powerful to God because it has always been and still exists to this day. If your friend believes that God is perfect, then the only conclusion left, is that your friend's belief is contradictory.

If your friend doesn't believe that God is perfect then it is because he doesn't know God, which means he himself is lost.
If this is the case, I would do some serious praying for him so that he may find salvation. I am sure you are praying for him already.

If your friend says, "OK evil had a beginning", then ask him to explain where it first came from.
Also ask him what God is going to do with all the evil that exists. Will God turn a blind eye and sweep it under the carpet. Or will He let it exist forever. Perhaps God will collect it all and throw it into his big rubbish tip. One of the names in the Bible for hell is "Gehenna". The name Gehenna derives from the name of a rubbish tip that burned day and night outside Jerusalem. It is logical to assume that God will throw all rubbish into his rubbish tip which happens to be called the "Lake of Fire". Remember that God cannot tolerate evil as He is pure and holy and sin is rubbish to God and even our righteousness is filthy rags to him.

Isaiah 64:6 (English-NIV).
All of us have become like one who is unclean, and all our righteous acts are like filthy rags; we all shrivel up like a leaf, and like the wind our sins sweep us away.

The only physical proof that Hell exists is discovered when one dies. We either go straight to Hell or Heaven. Hell is not a disputed fact in Heaven and of course if you are an unbeliever when you die you will go straight to hell and you will then become a believer, but of course it is too late. There is no repentance left.

The earth that we live on has both the nature of Heaven and the nature of Hell. There is good and bad existing side by side, righteousness and wickedness, light and darkness, truth and lies and both wisdom and foolishness. It's not so hard to believe that God is going to separate all these things when we die and that we will have one or the other depending on what we choose in this life. In fact that sounds very fair to me.

Believing in the existence of Hell is part of having Godly Faith. Faith in God aligns us with the truth of God. If we reject God's truth then we are rejecting God himself and such a person is expressing the nature of the Devil. We must believe that God is just, and that he will punish sin.

The Bible says that Satan is the originator of evil and that he was created perfect in the beginning. So evil originated in one of God's creatures and not from God himself.

One of the ways that the invisible God shows himself to us, is through his creation, see Romans 1:19-20 (English-NIV)
19 since what may be known about God is plain to them, because God has made it plain to them.
20 For since the creation of the world God's invisible qualities, his eternal power and divine nature, have been clearly seen, being understood from what has been made, so that men are without excuse.

In the same way we can see the existence of the Devil because we see sin and evil everywhere.
All we have to do is watch the news or even just walk around the area you live in. It is all around us. There are even many people that follow Satan knowingly. You also have to wonder who or what is blinding us from knowing God. The existence of God is actually quite obvious, but what stops us supposedly intelligent beings from seeing the obvious. According to 2 Corinthians 4:4 (English-NIV) it is Satan.

The god of this age has blinded the minds of unbelievers, so that they cannot see the light of the gospel of the glory of Christ, who is the image of God.

If we were to deny the existence of Hell and Satan, then we would have to believe that the Bible is unreliable and Demonic Possession is a figment of ones imagination. It would also mean that Jesus death on the Cross was meaningless as he supposedly died to save us from hell and to destroy the works of the Evil One. In fact the whole Christian faith would be pointless. This would also mean that we could all live very evil lives as there would be no punishment. I don't think a just and Mighty God would allow evil free reign with no punishment. What about all the people that suffer because of the sins of others. Did Adolph Hitler get away with his crimes against humanity ?

If we humans decided to abolish all prisons and punishment, then it would obviously lead to a world of chaos as people would would no longer fear retribution for their crimes. In fact if such a decision were made I am sure that even your friend would see the foolishness in such a move. Well, why would God do this. If we sinful humans punish sin for good reason, then why would a just and mighty God let sin go unpunished. If we escape punishment for our sins, it is only because Jesus took out punishment upon himself. Remember that Jesus suffered for our sin, so that we could go free. But we must be in a state of repentance to receive forgiveness.

I think that your friend needs to except the reality that Hell exists and Satan is the Lord of evil. It is Satan that blinds people to this reality so that he makes it possible for people to believe that sin is OK. But sin is not OK. God abhors sin because He is holy and perfect. He will throw all sin into Hell to await the great and mighty day of Judgment.

Revelation 20:12-15 (English-NIV)
12 And I saw the dead, great and small, standing before the throne, and books were opened. Another book was opened, which is the book of life. The dead were judged according to what they had done as recorded in the books.
13 The sea gave up the dead that were in it, and death and Hades gave up the dead that were in them, and each person was judged according to what he had done.
14 Then death and Hades were thrown into the lake of fire. The lake of fire is the second death.
15 If anyone's name was not found written in the book of life, he was thrown into the lake of fire.

If we do not believe in the existence of evil, punishment for evil, or that evil had an origin, then how do we explain or justify the holocaust, rape, murder, torture or poverty. We would have to assume that these things were normal and that they have a right to exist, yet our conscience condemns such things. Deep down we all know such things shouldn't be, but happen because something is wrong.

I think it is important to point out that the Bible shows us from this scripture that Hell is not forever as some think, but rather it is thrown into the lake of fire after the Great Judgment.

In Revelation 21:8 we are shown a list of the people that will be thrown into the Lake of Fire to suffer destruction.
"But the cowardly, the unbelieving, the vile, the murderers, the sexually immoral, those who practice magic arts, the idolaters and all liars their place will be in the fiery lake of burning sulfur. This is the second death."

Notice that the unbelieving are second on this list.