Maybe I can help explain the reservations many Christians have regarding Jesus Christ Superstar
by summarizing first the writings from which the play's story is derived, and then the play itself:
Jesus of Nazareth, the preternaturally self-assured, miracle-working leader of a popular Jewish revival, comes into conflict with the leading religious authorities of his day by his radical proclamation of God's coming kingdom and his claims, expressed both through words and actions, that he is not only the foretold Messiah of prophecy, he is in some sense identical with God himself. His torture, crucifixion and death at the hands of his enemies, treacherously aided by his own disciple Judas Iscariot, scatters his followers and all hope seems lost. But on the third day after his death Jesus rises from the grave as prophesized, finally revealed as Christ, Lord, and Savior. His suffering and death has brought atonement between humanity and God, and won a final victory over evil. The story ends with Jesus commissioning the disciples to spread the news about what has happened, upon which he ascends into Heaven.
Jesus Christ Superstar
Jesus of Nazareth, the doubt-ridden leader of a popular Jewish revival, is killed and his movement all but destroyed because his own Messianic delusions lead him to ignore the sensible advice of his disciple, Judas Iscariot. Judas is forced to betray his master to the authorities in order to prevent Jesus' followers from rising up against Roman occupation forces, an event which would spell doom for the Jewish people. Though his motives are worthy Judas is wracked with guilt over his treachery and hangs himself. The play ends with Jesus hanging dead on the cross and his disciples scattered and in hiding.
Those who believe the statements found in the Christian creeds would naturally disagree with any representation of Jesus as something other than what the Gospels, Acts, and Epistles say he is.
But I believe that what really chafes our butts in particular regarding JCSS is the way it has captured the popular imagination as being the "real" Gospel story (see Lumpy Fred’s accusation that our ire is rooted in our own ignorance of the Bible’s contents) whereas in reality it simply ignores those parts of the Bible which contradict the authors’ conviction that Jesus was just another doomed idealist who got carried away by his own hype. No miracles and no resurrection, which makes Jesus' claims ridiculous.
Which is fine. If you think Jesus was a fool, so be it. But please, please don't play it back to us like you're paying him some sort of compliment.
Oh, and some folks think that rock music is Satanic, so they don’t like that part neither.
(On a personal note, I gotta confess that in spite of my objections to it, JCSS is something of a guilty pleasure of mine. The songs are catchy, and when you have the right guy playing Jesus it can be magic.)