1) No it does not have to be said. Nobody is forcing anyone to explain anything.

2) I think that the best satire is fair, and should read to the targets as real commentary. When someone takes your satire seriously, it means that you have successfully commented on reality. Is that inverse Poe's Law?

Otherwise you're just putting words in your enemies' mouths that they would not ever say. I think people do this because they don't have the strength of their own convictions, and wouldn't be able to stand people not getting their joke (and worse, confusing them for extreme believers in something that they disdain.)

To them I would suggest that one doesn't try to make arguments through satire, one rather demonstrate arguments through satire. If you need to make your argument with satire, you actually don't have an argument. Satire without a solid underpinning argument is just propaganda.