As angry demonstrators clogged streets and shut down highways and bridges in New York, Chicago and San Francisco on Thursday, New York City Police Commissioner Raymond Kelly said that this generation of antiwar protesters has become particularly vicious."There is a hard core group.... who are particularly nasty," Commissioner Kelly told WOR Radio's Bob Grant. "I've noticed this and I've been around a long time. It's kind of like the Vietnam war protests."Kelly complained that the anti-Iraq war protesters had engaged in acts like "spitting on police officers, cursing at them, trying to instigate them." He added, "It really is a disgrace for people that supposedly want peace.""There are police officers who are out there trying to do their job, trying to protect people's liberties and rights to voice their opinions," New York's top cop explained. He might have also noted that New York's finest sacrificed 23 hero cops in the 9/11 attacks.He said his police force had shown "tremendous restraint" in dealing with the hostile peaceniks. Still, "there is this hard core group of demonstrators (and) they're there to cause problems," Kelly told Grant.