One of the primary reasons why skeptics date the gospels later than 70AD is the fact that Jesus predicted the destruction of the Temple in the gospel accounts (i.e. Matthew 23). Secular history records that the Temple was destroyed in 70AD, fulfilling this alleged prediction by Jesus. In order to avoid the accurate prophesy from Jesus, skeptics argue that the gospel must have been written after the temple was destroyed.After all, how could Jesus possess the supernatural power of prophecy if nothing supernatural exists? The philosophical naturalism of the secular historian prevents him from accepting the possibility of accurate prophecy.
The gospels also contain many descriptions of miracles. The philosophical naturalist must also deny the truthfulness of these supernatural accounts. Skeptics, therefore, date the gospel accounts very late, arguing that eyewitnesses to these events were already dead and unavailable to deny the claims. It turns out that the presupposition of philosophical naturalism is at work in the minds of those who would deny the early dating of the gospels.
When this presuppositional bias is removed, the remaining evidence confirms that the gospels were written in the lifetimes of the eyewitnesses.