Perhaps not, but the majority of if not all the planets that are known by astronomers are utterly inhabitable for one. Second, just as it is possible for life to exist in other galaxies far away, it is possible Earth happens to be extremely fortunate to have received the necessary elements over billions of years to produce life in the way of organisms. Additionally, it is also possible that we are but the last living organisms with the ability to think within our given solar system; Why? Look at the moon and tell me what you see....infinite amounts of craters. Life on this planet may end at any given moment without prior warning or any means of preventing it. Even the destruction of the Earth's moon would yield the key to the destruction of all humanity and life as we know it.
Anything unusual and unrecognisable can be thought to be alien, if you present it correctly.
40 years of intensive searching for extra-terrestrial intelligence have yielded nothing: no radio signals, no credible spacecraft sightings, no close encounters of any kind.
Now...only to make by beliefs and ideas clear here: Briefly and in short, I do not believe there are other beings out there anywhere (period) with capabilites such as those we humans have inherited which are the abilities to think & reason. However, I can not honestly say that there are no living organisms in an galaxy or our universe...only that if any they do exist then they are likely small non-thinking creatures such as fish-like organisms.
Since it is perhaps one of the most common human characteristics and traits to question, inquire, imagine, etc., to perceive that there are "aliens" is perfectly natural of homosapiens.