Explanation:
This is an example of groupshift.
Groupshift can be described as the gradual inclination of group members toward extreme positions from their initial views. This happen by continuous positive reinforcement of the general group opinions.
Individuals often look up for conformity from other group members. As a result their choices, mindset and decisions are influenced by that of the consensus of the group. This gives rise to bandwagon effect. For example, a group of women rights activist may turn to extreme feminists or a group of mildly racist people may end up becoming extremely racist.
Similarly, in the given scenario, Dan's views were further amplified by being with like-minded people.