According to a new study, it seems to depend on how big they are:
Michael Varnum, a psychologist at Arizona State University and a member of its new Interplanetary Initiative, is trying to anticipate this response.
The scientists asked 500 people to describe their reactions to a hypothetical discovery of alien microorganisms. Respondents also had to predict how humanity at large would react. Like the journalists, people in the study used positive words. There were no characteristics that set responses apart, not a person's income, ethnicity, political orientation or traits such as neuroticism or agreeableness. But people felt that the rest of the country would be generally less agreeable.
That may be because “most Americans tend to think, on any desirable trait or ability, that they're better than the average person,” Varnum said.
So tiny aliens are OK, but larger ones are scary? Has no one read The Andromeda Strain?