Headscratchers: The Day the Earth Stood Still (2008)
Why did the "advance scout" declare humans purely destructive and in need of being killed off, then insist that they have a good side to them?
The advance scout reached his conclusion very quickly, after calculating how long it would take before the Terran ecosystem was irreparably damaged, but was slowly influenced by his own new human emotions, effectively deciding "anything that feels this good can't be all bad".
Why does Gort open his visor only when he's attacking things in the arrival scene, shutting it down when he's standing still, and then proceed to spend half the movie using it to glare menacingly at people? For that matter, why does giant-robot-Gort exist at all if it's cloud-of-nanobugs Gort that's going to do all the work?
Gort's visor serves the same purpose as his robot form: intimidation. He stays a giant robot most of the time because it's more impressive, then disassembles into the swarm when he doesn't need to be scary anymore.
Why can Klaatu barricade off a small area from the nanobugs, but not create a safe zone around himself to approach the sphere? For that matter, if the aliens want life to survive on Earth, shouldn't they have an OFF SWITCH for the nanobugs? And so on.
Klaatu's barricade may have been merely taking advantage of the swarm's behavior: they're programmed to eat easily accessible things before attempting to fly through small spaces to reach less accessible things. That, combined with a signal such as "this area has already been cleaned" could have kept them away at least until they had finished eating everything else nearby. However, he couldn't use such a signal to designate an otherwise unobstructed area as off-limits. Likewise, the swarm was most likely programmed to stop once it had eaten enough to to remove the danger to the ecosystem, but leave enough for the planet to regenerate eventually. This may have consisted of eating all animals, all animals above a certain weight threshold, anything with a notocord, etc. Alternatively, it could be programmed to eat all the biomass, then use most of that to restart the biosphere (presumably in a way that would allow eventually colonization but wouldn't lead to the native development of sentience.
If inhabitable planets are so rare, wouldn't thousands if not millions of aliens be studying us around the clock for at least several years, not one advance scout for 40 years to be interviewed by one later scout for 5 minutes, who then unilaterally decides to destroy everything?
This is pretty much explained in the movie. Pretty much every space faring race (at least near enough to know of Earth's existence) is part of this collection of Civilisations that Klaatu refers to. And as stated by him, they've been observing humanity's progress for a very long time watching and waiting for us to 'clear up our act'. It was only those few (perhaps more than the one Chinese man) that chose to live among us felt the depth and breadth of Human emotion. But from those only observing from the afar, it was our aggression and selfish nature that defined us, and could no longer wait, action had to be taken.
What's a biologist doing figuring out advanced relativistic physics equations?
Why does Jacob, a child who constantly goes on about how the aliens should be wiped out because they might be a threat, draw nary a notice by his mother or Klaatu for what he's saying?
I was thinking about this as well, she could've told Jacob something along the lines of "There's no reason to fight someone if they don't want to hurt you" or something. But I figured she mostly stayed quiet because she didn't want Jacob to realise that Klaatu was the alien, which he eventually does anyway.
These aliens, who clearly are using their own advanced technology, demand that Earth stop using its electricity. Hypocrites
Even worse, when the scientist asks why can't the aliens just give us clean technology, Klaatu says that technology isn't the issue and it's because we refuse to change. Uh, we haven't changed because we don't have a clear alternative to change to. It's not like the solution to all our problems is sitting in our laps and we're just being stubborn assholes; it's because we see the need to change but have yet to figure out how and manage the turbulence in doing so. Even Klaatu handing us the technology on a silver platter will severely screw our economy as oil and coal become obsolete. Do these aliens even understand the concepts of 'economy' and 'infrastructure'?
You kind of answered your own question at the end there. But I felt it was heavily inferred that if they do hand us say, a source of clean and infinite energy, what would we do with it? Privatise it? Weaponise it? As you said, giving us this technology will do more harm than good.
Also, these aliens believe that we're destructive and warlike, and so decide to utterly wipe us out with flesh-eating nanomachines. Damn hypocrites.
Well, we're not ment to agree with them.
We're not? The impression I got was that we were meant to agree that we should probably die for our evil warlike polluting ways, but oh well, there's no superadvanced alien homicidal maniac ecoterrorists around to do it.
If you're trying to save the natural environment, why do you shut down all of humanity's advanced technology, forcing 3-4 billion humans to go out into the countryside and eat anything that moves and burn anything that burns in a desperate bid for survival?
Not to mention that some things need power to keep running or otherwise very bad things will happen. Chemical processing plants? Nuclear reactors? Liquefied natural gas? Those need human maintenance and other sources of energy to keep running properly or they'll deteriorate. Hope the environment likes chlorine gas and nuclear radiation. (See here.)
Why didn't the military once try nuclear attack on the swarm? Given the EMP ending, we could've had the same result with much less catastrophic effect on the planet.
if the blast were low surface instead of high atmosphere, the EMP damage wouldn't have been that much.
But what commander is going to order a nuclear attack on his own country?
In the grand finale, Klaatu shows mercy on humanity but completely shuts down technology with an EMP blast that covers the entire planet (or at least a very large radius) presumably to prevent humanity's science from further harming the planet. How many deaths is everyone willing to wager emerged from downed airplanes, doctors currently performing operations and people with pace-makers at the time? And what's more, how much of a negative impact is everyone willing to bet effects humanity's future considering our major dependence on technology to keep our society going?
Exactly. Yes, overuse of certain technology is bad (I think we can all agree it would be stupid to use high-tech nukes all willy-nilly). But, a huge percentage of technology today is necessary for human survival. Disabling all technology would cripple modern communication (Especially in cases where people need to pass on information to one anothr and as quickly as possible), medicine, and defense. Taking away all technology would set humanity back to the Stone Age and would cripple the species as a whole. There's a big difference between learning how to be responsible with technology and wiping out devices humans need to survive.