@naomi
Thanks for this thread. I have to say that was probably the first time I've read a news article where the comment section was more entertaining, informative and, in several instances, voluminous than the news piece itself. (Slightly unfair as it was basically an overly wrapped link to the featured author's full-length work).
I would like to go on at length about convergent evolution but you've made it clear that (the science) is outwith your planned scope for this thread. Fine, although I still wish to point out that he appears to be invoking it on the basis that the ecological niche for "bipedal hominin with opposable thumb and high mental capacity" is a universal thing: an "end goal".
Oh dear, what a giveaway. He's in the intelligent design camp.
I might concede that the 4-limb body plan (imho) was arrived at because 4 fins, plus a tail and a dorsal fin was the *minimum* that fish needed for fine control of movement. At the amphibian level, 4 limbs can clearly outrun 2 limbs and hunt it to extinction. 6 limbs might appear to be even better but requires more food resources to grow. Population growth would be slightly slower than 4-limb ones and survival is a numbers game, in the long run, so whichever breeds fastest, using the minimum amount of resources to do so, tends to dominate.
In other words I concede that physical laws, concerning the conversion of foodstuffs into populations will favour the bodyplan we ended up with but who is to say that life on other planets will even take the vertebrate route at all?
One of the comments sagely touched on the fact that you need fire to smelt ores into metals and that would not be feasible on a planet with a methane-rich atmosphere. A convoluted way of hinting that life can evolve as far as intelligence but there may be obstacles to technological advancement, to the space-faring stage.
Your true OP question strikes me as convoluted. If we find life in other star systems, we cease to be 'special' in the universe and it would strike at the validity of the faiths. The converse of that is that we are special but, horribly, alone in the vastness of the void.
Then you leave the door open for theists by suggesting that religious figures might be hopping around the universe, spreading their message. Lacking the constraints of corporial form, they should, notionally, be able to do this.
Or (shudder), heaven is outer space and we all become door-to-door (ie planet-to-planet) salespersons. No wonder the faiths try to recruit us by the billions!