The argument “The universe is so big that life must exist on other planets” is kind of silly. It's like saying “this hardware store is so big there must be a watermelon down one of these aisles”. That said, inter-dimensional life does exist by many accounts and that includes both positive and negative entities.
As a Christian I'm obviously inclined to think that some of these beings are demonic and they lie through channeled messages and push people to perform occultic practices to get in touch with them. At the end of the day it draws worship away from Jesus Christ, confuses people with false signs and wonders, and opens them up to demonic attachment. It's a nice little scam these beings have going frankly.
On the flip side there are angelic beings and despite pop culture depictions of winged beings with cherub-like features they look very 'alien'. Beings of light, human-like creatures, and creatures that are so incredibly 'other' that they defy explanation. From my own personal experiences and encounters as a believer that is more mystically and prophetically inclined I can say that some even travel in strange craft as well which seem to act as vehicles which radiate the glory of the Lord. When it comes to the spiritual realms almost anything goes.
I am however less inclined to believe that flesh and blood aliens exist. I suppose it's a possibility and frankly it fits as something we should expect from a God that loves to create, as evidenced by this seemingly lonely planet teeming with biological life. On that same note it's also entirely possible that God wove together this grand cosmos just for us in order to magnify His glory and demonstrate His awesome power to us and us alone. Personally I want there to be life on other planets and, as I mentioned, I kind of expect there is because of who I know God to be. Regardless, there are spiritual realms beyond sight that are already bursting with unique intelligent life.
My suspicion is that any 'disclosure scenario' we find ourselves in that purports contact with flesh and blood aliens will likely be the product of sophisticated cloning techniques that produce strange human-like or chimeric entities. Anyone that has been following UFO lore for any amount of time is aware of supposed 'programmable' life forms and holographic deceptions. I do hope I'm wrong about this.