Everything Apollo-believers present as proof has alternative explanations.
Irrelevant. One may always speculate about other causes for observation besides the proffered or commonly held one. The ability to do that does not itself challenge the prevailing view. In order to show that some new hypothesis should prevail, one must show it explains the evidence better than the prevailing one. Noting that hypothetical alternatives exist is not probative. It is tantamount to setting the standard of proof at the level of proving it is impossible for something to have occurred any other way, not merely that it didn't occur any other way.
One piece of solid proof that they didn't go is all that's necessary.
The Bellwether fallacy (a special case of the Fallacy of Limited Scope). You must, in fact, explain all the evidence that supports the conclusion you disagree with, because only then does it become a rational theory. You cannot simply suppose there must be some reasonable explanation for all the evidence if you predicated your theory solely on one piece.
The bottom line is that the flag wouldn't have moved like that in a vacuum.
Begging the question.
If they had really gone to the moon, there would be a ton of proof that they really went...
There is. You're trying to explain it all away. That exercise presupposes its existence.
...and no proof that they didn't go.
You have provided no proof that they didn't go. You have merely speculated about other ways in which you think the evidence could have arisen that the did go.
If you think there's something that proves they really went, please post it and we can talk about whether it's really proof.
You are the one claiming it was hoaxed. You have the burden to prove it was hoaxed. Merely speculating other ways in which the evidence may have arisen that they did go does not meet that burden of proof.