Renown British scientist Stephen Hawking's decision to cancel his participation in the President's Conference is "a slap in the face to academic freedom," the Anti-Defamation League (ADL) said in a statement on Wednesday.Hawking withdrew from the conference after Palestinian colleagues urged him to join the academic boycott on Israel."It is sad that a man of Dr. Hawking’s immense intellect is unwilling to see the double standard and demonetization which are the hallmarks of this anti-Israel movement," ADL National Director Abraham H. Foxman said."Hawking has joined a relatively small group of closed-minded academics, entertainers and other public figures who show their lack of respect for academic freedom and the promotion of the free exchange of ideas," he continued.