"Invasion" by Frank Belknap Long
Background
In “Invasion”, Martians visit the Earth and use as messengers humanoid automatons featuring the best we look for in ourselves. One messenger arrives at the home of an average family that accepts him with open arms. However, once the authority figures arrive things get out of hand. Mayor Bowers emerges, shotgun in hand, and accuses the Martian of coming to invade and conquer Earth. He has no evidence to this effect, but the supposition is strong enough that he shoots the Martian in the chest when he refuses to enter police custody. As a result the Martians are unwilling to show themselves in their true form to a race that treats its own kind so poorly, and we lose the gift of immortality due to Bowers's xenophobia.
Analysis
Long's story, while somewhat hastily written, is an excellent example of what can happen when people make hasty judgments based on race—when we, in effect, judge a book by its cover. Bowers is a flat character, but in that sense he is very indicative of many humans when it comes to trusting outsiders—very rarely are we willing to see both sides of an issue. Bowers was probably the most believable character in “Invasion”. Everyone else trusted the alien far more easily than an open-minded reader can imagine a family would have.