I probably gave my opinion on this thread before, but I'll go ahead and do it again since it's been a while.
Yes, life exists out there. But this doesn't mean it's going to be similar to our idea of life. Organisms on earth all evolved in a similar environment, meaning they share a lot of very similar traits that people take for granted. For example, most land organisms share the common traits of having eyes near their mouth, nose, and ears, altogether constituting a face which is common among most organisms. Even fish, which evolved in an underwater environment as opposed to on land, share these traits. Now, consider a completely different planet where conditions are vastly different from on earth. Organisms adapt in different ways to suit this environment. Evolution itself is a process that operates at the most basic level purely on chance, so there's always the possibility that organisms on a different planet took a different path in their evolution, even if the conditions were the exact same as on earth.
What I'm getting at here is that life on other planets could develop in a way that humans might not even recognize as life. Perhaps aliens on another planet are autotrophs, like plants, and never develop the need for mobility, so they don't need any central nervous system to coordinate motion, meaning they have no brain. Perhaps aliens develop a different way of obtaining their food than humans, so they don't need visual organs or a sense of smell or taste or anything. Who's to say that they create proteins using RNA like we do, and who's to say that they use DNA as a way of mapping genes? Who's to say that they even pass on genes at all? They developed in a different environment, so anything could happen. The idea here is that alien life itself is very likely to be so vastly different from us that we wouldn't even consider it living at first just because the aliens develop in a different environment that creates different rules on life.
Assuming that aliens were similar enough to humans to be recognizable (which is already infinitely unlikely for the reasons stated above) their culture would be so different from ours that we wouldn't be able to communicate or see eye-to-eye for that matter. Perhaps in this alien society, domestic violence is welcomed and shows strength and valor among its people. There's no way we could ever abide by those cultural implications, and there's no way the aliens would change their entire cultural ideas just to conform to ours. This is just one of many examples of how alien culture could be different from ours. There's only an infinitely slim chance that aliens could be similar enough to us that we could communicate effectively.
Saying that alien life exists is like saying that there's a needle in a haystack. It's true, but it would be so impractical to find that we might as well just not consider it.
