Whilst I am convinced that life exists elsewhere in the universe as part of the natural process of planetary development I do wonder why our alien visitors always seem to be vaguely humanoid.
There are about, or at least, ten million different species of living organisms on Earth varying from bacteria to blue whales (without getting too hung up on the classification). There is also huge variation within single species - dogs for example, ranging from chihuahua to Great Danes. There is even huge variation between the sexes of the same species; birds (peacocks/peahens, birds of paradise) where the different sexes have sometimes been counted as different species; fish - the male angler fish is one fiftieth the size of the female. The list is endless.
Yet all alien visitors look like humans. Maybe grey or green, maybe taller, maybe smaller but humanoid nonetheless.
Strangely enough they also mostly look like aliens out of old sci-fi films.