Consider the following facts. Jesus Christ claimed to be the promised Messiah of Old Testament literature. There is no middle ground. A matter is true or it is not true. The claim that Jesus here made, of being the Messiah, was, therefore, either true or not true.
Logic demands that.
If Christ was not who He claimed to be, but rather was a deceiving charlatan, He becomes one of the most despicable characters ever to disgrace human history. Multiplied thousands have gone to their deaths for their belief in His claim. He must be condemned. If Dershowitz reasoned logically, he would be obligated to denounce Jesus Christ as an imposter. He would not praise the Lord in one breath, and disown Him as Messiah in the next.