Depends are we talking any form of life or 'intelligent' space-faring races?
In truth, just due to the sheer magnitude of the universe, no matter remotely small the odds of life, even intelligent life, it is absolutely guaranteed to exist, somewhere, somewhen else in the universe.
If someone rejects life of any form existing in the universe - then they are burying their heads in the sand and ignoring simple facts and math. It MUST exist. It's impossible not too. And really, that doesn't conflict with anyone's belief system either so it doesn't matter if they are Muslim, Christian or followers of Zeus (which do still exist, believe it or not) this shouldn't challenge their faith or sensibilities so if they reject it they are very closed-minded.
If they reject the Star Wars/Star Trek concept of alien life, that's fine. It is indeed out there somewhere but Space is so large we might never, ever come across it in humankind's existence and that alone is enough cause for them to disbelieve. For example the next 'intelligent' life might be in the Andromeda galaxy - an inconceivable distance away - and likely our species will never even know of each other.







