They have to stand in the way because they arent right. It is obvious that there is extraterrestrial life out there.
It takes religion to make you arrogant enough to think you're the special one.
Now wether we will be able to meet some other sentient species is a more difficult challenge. We need to develop better space traveling methods to be able to see them. Unless they are more advanced and find us first.
Also, its very likely we will find a non sentiant form of life as close as Europa, the moon of jupiter that seems to have a global wide ocean under the ice. And where there is water, there is usually life. If you think about what kind of beeing we are and how complex nature made us, the chances that many other variations in many other environments exist is likely.
If like can be found more than once in the same solar system, it might not be such an unlikely occurance.
