1. "258 witnesses were discredited - most of whom said they saw a streak of light leave the ground and strike the plane."
Off all the witnesses interviewed 183 say they saw a streak of light. Of those, 96 say the streak originated from the ground. Of those, 40 say it originated from the water and 10 said from the land. None of them reported seeing it "strike the plane".
2. "And most of those people were very credible - pilots - military - people in sciences who understood what they were seeing."
Very few of the witnesses to the event were anything like what you just described. With the exception of an ANG helicopter crew, none of the airborne witnesses (26 total including several airline pilots) reported seeing any streak at all. Your statement is simply false.
Then there's the EastWind Air pilot who was looking right at Flight 800 when it exploded. He reported no missiles.