Your right... we cant assume their physiology... or for that matter, their motives, their drives, their technology or their behaviours. In other words, we have no idea what they might be like. There are gazillions of possibilities.

For instance you speak of internal fractions... that again is an example of anthropomorphising.... they may be a monolithic society with no internal factions... they may be a hive... who knows.

The point is that what you refer to as an educated guess is, in fact, our uneducated guess based on a sample size of one. In no way is that a basis to form a policy... apart from... lets be cautious.

Some folk like to talk about evolutionary pressure and behaviours as though we have enough of an idea from earth-life what broad sorts of behaviours we will see in aliens.(if they exist). I would suggest that most of us (especially me) don't even know the tiniest fraction of the different sorts of behaviours available (and used by) even earth life-forms.

It is entirely possible that they will be human like with slightly differing eye colour.... but my bet would be that different circumstances will produce different answers to the problems of life.

Look at us.... we are fish. All of our (and most other animals) morphological features hark back to (at least... and possibly earlier) the earliest finned fish we know... the sharks. Look at symmetry... a nearly universal principle here on earth. I will bet it is built into your subconscious views of alien morphology. But it could be a purely earth based feature... and its presence or lack could have startling effects on all sorts of behaviours.

Often we are like English gentry of the 19th century considering that all the 'natives' of the world are uncivilised... our world view is way too constrained.

My point in all this is lets be cautious... lets stop astronomers from periodically shouting out to the universe... 'Come on by and stop in for dinner....'