I agree with you, but I think it's worth remembering/noting that this happens mostly because it's very difficult if not impossible to imagine what a sentient being with a psychology entirely unlike our own would be like.
I think that most people (who think about such things) realize that extraterrestrials, if they exist, may well be more alien than we can even imagine.
But it's fun to imagine things, so we try anyway :)
For instance, try to imagine a new emotion that is not a composite of the emotions you have.
We know animals have emotions, and they mostly map to our emotions. With less related animals likely having less related emotions to ours (like the emotions of a tuna fish compared to a chimpanzee).
Now, try to map the emotions of life-form that from a completely different tree of life from ours. Their version of emotions may not even be mappable to anything like we can ever experience or imagine.
Emotions are pretty core to our understanding of the universe and ET may have emotions so radically different to ours that their view of the universe is not understandable to us.
I agree. But at the same time, some things can be quite common across the universe. For example, evolutionary processes that arise due to competition in an ecosystem lead to certain traits (conservativism, being vigilant all the time, etc.) which could be common across life-forms that have very dissimilar trees of life. For instance, think of how birds, deers, and butterflies react to dangers around them. We as humans can relate better to deers and birds, but not so much to butterflies. Nonetheless, all of us share the same "fear" about surrounding movements and that has influence on our emotions and character.
I think that most people (who think about such things) realize that extraterrestrials, if they exist, may well be more alien than we can even imagine.
But it's fun to imagine things, so we try anyway :)