This is due to the fact that most people no longer see the Bible as inerrant or infallible. They don't even see it as God's written Word. They believe that it contains God's Word but it is not God's Word. It is "inspired" as any other wonderful piece of literature (Shakespeare, the Koran, etc.). If they truly believed the Bible as the inerrant written message from God then they would never question the holiness or deity of our Lord.
The Bible is clear that Jesus never sinned:
For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin. (Hebrews 4:15)
For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him. (2 Cor. 5:21)
And ye know that he was manifested to take away our sins; and in him is no sin. (1 John 3:5)
For even hereunto were ye called: because Christ also suffered for us, leaving us an example, that ye should follow his steps: Who did no sin, neither was guile found in his mouth: (1 Peter. 2:21-22)
For my part, I believe what the Bible says without question. He never sinned and because He never sinned He was able to redeem me from my sin. I sinned but He didn't and His never sinning gives me the power over sin and wipes away the record of my past sins.