They are close to us just because of costuming budgets, and to make them more accessible tp viewers - though the being in the first episode of ST:TNG, for instance wasn’t like us at all.
It is unlikely that a being 1/2" in height is going to have the brain volume to be very intelligent - unless is was like a Mesklinite and was short but long. Large beings are not going to be able to develop in gravity fields that hold an atmosphere, and in any case the propagation delay between brain and organs in something that big is going to be evolutionarily disadvantageous. There will be more variance, no doubt, than shown in the movies, but not that much.
There was one episode (don’t remember the name, Norman Lloyd was a guest) where it was explained that all of the major races had a common ancestor that seeded the planets before they ascended to a higher plane or something. Funny how something that important was never mentioned again.
One of the first and most famous extraterrestrial invasion stories is H.G. Wells’ “The War of the Worlds.” Wells, writing in the 19th century, did not make his Martians vertebrate, much less humanoid.
Lovecraft, in works published between 1917 and 1935, gave his extraterrestrials, the Old Ones, a variety of appearances: a vast cold flame; a slimy mass covered with eyes and mouths; a giant spider with a human face; a gigantic eye covered with tentacles; a pale, gelatinous oval with many legs and eyes; a shapeless, inky mass; etc., etc., etc.
Even cheesy sci-fi TV show “Lost in Space” had a cosmic energy being in its first season.
“Star Trek,” the original 1960s series, had an 18,000-mile-long space amoeba, various energy beings, parasitic creatures resembling oversized brain cells that were somehow linked in a collective consciousness, a gaseous cloud, intelligent rocks, a literate acid-secreting silicon blob, tentacled and telepathic brainlike creatures, and tiny but mentally powerful ornithoids.
There are also many examples in science fiction of non-humanlike aliens assuming or projecting a humanoid appearance in order to interact with humans.
Or unless whatever it uses as neurons is much smaller; molecular “circuitry” instead of relatively huge whole cells, say. Although a 1/2" sentient is pushing it I admit.
Not all things scale in the same way. your 1/2 inch aliens would have a harder time smelting metals during their pre-industrial phase - they would have a hard time controlling fire in the way we do, hard materials like stone and metal would be difficult to work, and so on.
Different approaches to the technologies might still prevail, but the point is that inch-high human-like aliens would not be able to do the same things that humans can.
Convergent evolution. You see it here on earth. Bats, birds and have wings with similar structure but they are not evolutionarily linked.
Bats and birds evolved on the same planet with the same atmosphere, temperature ranges and gravity. IRL, it is unlikely that aliens would look anything but vaguely humanoid as their planet could be significantly different.
Keep in mind that science fiction bears no resemblence to reality as alien biology is normally constrained by budgetary and plot concerns.
The thing along those lines that irks me is when the aliens tut-tut about how violent and destructive humans are, what with almost destroying ourselves, building nuclear weapons, etc.
We’re violent because that’s the character that we ended up with after millienia of natural selection. Why assume that aliens would be any different?
Maybe monkeys that would have the temperment to evolve into peaceful logical intelligent beings always get eaten by the meaner monkeys.
On the plus side, they would live in a world with a far higher amount of space and resources relative to themselves ( ore deposits aren’t going to shrink just because the aliens are tiny ). And such things as flight and space travel would be much easier achievements for such tiny, low mass beings. They’d probably have higher tolerances for g-forces as well.
Actually, there are non-violent monkeys; I don’t recall the species name but they are large ( for monkeys ) and live high in the treetops where branches are thin; fighting is an invitation to falling to their deaths. So, they have evolved to be nonviolent because the violent end up dead.
The funny thing is, HUMANS are actually quite peaceful compared to most animals. When you count acts of violence, “peaceful” animals like deer are a lot more violent than humans. It’s just that humans are much, much better at it. In fact, that’s probably WHY we are less violent - over the millennia, the most violent have been weeded out by natural selection.
Personally, I think that an advanced alien race will be much less violent than humans ( at least to each other ) for just such survival driven reasons. They’d probably know that’s why they are less violent, though, and not be surprised that such a young species as humans are as violent as we are.