AThe Visitors, particularly Brian, were persuasive enough with a few collaborators (a group which also included Mike Donovan's mother Eleanor Dupres), convincing them that working against their own people would bring them prestige and power, perhaps even fame and money. Daniel joined the "Friends of the Visitors" group which is a parallel to Hitler's youth movement in Nazi Germany. He is later given a brown Visitor's uniform which is a reference to Hitler's famous "Brownshirt" paramilitary group, which aided him in finding traitors to the cause of the Nazis.
ABecause they were the group that would be most likely to discover the Visitors' real intentions. There are a few scenes early on where a few scientists, Julie is one of them, talking with suspicion about the Visitors' biology and how there's so little information about it & about the aliens' unwillingness to share very much about themselves. By discrediting and restricting the rights of scientists, and later hunting them, the Visitors would be better able to continue their insidious work of slowly draining Earth of it's water (their primary goal) and enslaving and using humans for food.The parallel with human history is that the scientists who are hunted and persecuted in this film resemble the races that were given the same treatment by the Nazis during World War II, most notably Jews, gypsies, Russians, Hungarians and many other ethic groups the Nazis found undesirable. The Nazis also murdered people who pursued intellectual interests such as music, art, history, philosophy, literature because they were suspected to be the most likely to rebel against the Nazis fascist rule.