Final answer:
A strong and directive leader in a group can unknowingly encourage group members to engage in self-censorship, which hinders diverse opinions and contributes to faulty decision-making.
Step-by-step explanation:
According to research on groupthink, one disadvantage of a strong and directive leader is that they may unknowingly encourage group members to engage in self-censorship. This means that group members may withhold their own opinions or information to avoid disrupting the group or going against the leader's views. By doing so, the leader suppresses diverse opinions and contributes to faulty decision-making by the group.