ARGUMENT 1: MEN HAVE WALKED ON THE MOON
Cynics have scoffed at the Moon landing right from the beginning. In December 1969, the very year it happened, the New York Times ran an article saying "A few stool warmers in Chicago bars are on record as suggesting that the Apollo 11 moon walk last July was actually staged by Hollywood in a Nevada desert".
From this initial acorn of doubt, a vast and multi-branched oak of bad science and paranoid speculation has grown over the years. Yet the main arguments put forward by conspiracy theorists can be shot down with ease. Take the question of the Van Allen belts. These are zones of charged solar particles held close to the Earth by our planet's magnetic field. Some say humans wouldn't be able to cross through the belts without getting a lethal dose of radiation, making a trip to the Moon impossible.
It's true that NASA was concerned about the Van Allen belts - which is why they cleverly plotted a path through the danger zone which minimised radiation exposure for the astronauts and ensured they were well within the safe limit, as proven by dosimeter readings taken by the crew.
Then there's the issue of the "flapping flag". According to conspiracy theorists, the US flags planted on the Moon by various Apollo crews can clearly be seen "flapping in the wind" - a dead giveaway that they were on Earth rather than within the vacuum of the lunar surface. Except that this "wind" is illusory. The flags only flap when the astronauts are trying to stick the flagpoles into the ground, and remain static afterwards. (The flags look rippled because of the way the fabric was suspended from the horizontal poles placed there precisely because the flags would otherwise droop down in the vacuum.)
How about the shadows on the lunar surface? Why aren't they EXACTLY parallel with each other, as you might expect from the single light source of the sun? Simple: the rough and rugged terrain of the Moon causes shadows to fall in varying angles, just like on Earth. What about the lack of stars in photos taken by the astronauts? Surely the sky over the Moon would be filled with stars, rather than the eerie black we see in the official NASA pictures? No, because - in order to capture clear photos of the surface itself - the cameras were set to a short exposure time, meaning they couldn't capture the relatively dim light of the stars.
There's also actual, physical evidence we were there. For example, footprints and other traces of the Apollo landing sites have been recorded by NASA's Lunar Reconnaissance Orbiter (and also by Japanese and Indian spacecraft, if you don't trust NASA). There are also thousands of Moon rocks, verified by geological analysis to not be of Earth origin. And anyone watching video footage of the lunar rover being driven about on the Moon will notice the way dust is kicked up by the wheels in a distinctive "rooster tail" shape, which Earth's greater gravity would prevent from happening.
Meanwhile, the Soviet Union, which was able to closely monitor the Apollo missions, never raised any doubts about the success of the lunar landings. In the time of the bitter Cold War, their acceptance of their defeat in the Space Race is perhaps all the proof we really need.
ARGUMENT 2: MEN NEVER WALKED ON THE MOON
Can anyone argue the Moon landings were a hoax, without sounding like a crazed, conspiracy theorist? Perhaps, if we step back a bit and consider the bigger questions. First: was there a clear and strong motive to fake the landings? Second: would it have been absolutely impossible to fake the landings?
The answer to the first question is definitively "yes". Putting aside our rose-tinted specs about Apollo 11 being a "giant leap for mankind", we can see how the project to put men on the Moon was driven by a ruthless competition with the Soviet Union. The Soviets had already scored embarrassing victories by launching the first satellite (Sputnik 1) and putting the first human being into space (Yuri Gagarin). For the US, getting to the Moon was about preventing Soviet domination in the Space Race, just a handful of years after the two superpowers almost wiped each other out during the Cuban Missile Crisis.
So yes, as far as the US was concerned, the clock was ticking, and there was every reason to fake the Moon landing if NASA lacked the capability to get there in reality. Would it have been possible? The truth is, we cannot rule it out. The Cold War was a time of immense secrecy, and it's difficult to definitely discount the possibility that film footage could have somehow been faked by a well-equipped studio.
Remember as well that this was an era of skulduggery at the highest levels of power. Think of the now-notorious MKUltra mind control experiments carried out by the CIA, often on oblivious US civilians. The Watergate scandal, which implicated President Nixon himself in dark shenanigans and brought down his administration, unfolded just a few years after Apollo 11.
Apollo believers often point out such a conspiracy would have been too vast to contain, with hundreds of thousands of scientists, technicians and assorted personnel having to swear to secrecy. But did everybody at NASA have to know the truth? What if the Saturn V rockets were simply launched into orbit, satisfying observers on the ground, while the mission control staff were unwittingly fed the fake transmissions? It's surely conceivable that only a small, hardcore team of black operatives would need to be in the loop.
Other aspects of the alleged landings can be cast into doubt. For example, the retroreflectors left on the Moon's surface, which are often cited as evidence of astronaut activity, could have been planted by unmanned probes. It's also curious to note that when China recently announced its intention to humans on the Moon by 2036, the announcement made clear they needed all that time to develop the technology to make it to the lunar surface. Isn't it odd that 21st Century tech seems to be lagging far behind what Apollo 11 achieved half a century ago? Food for thought...