You are correct, I should have prefaced my statement with, "I think" or "I like to believe." I happen to believe cynicism is a seductive methodology, while sometimes useful. I don't care for FB's hegemony either, FWIW.
I'm inclined to agree with you and the implicit assumption of good faith. However, FB's trend information is an instance of real power and susceptible to the sort of hiding of capabilities and intentions that implies. It's fair for people to ask for verification though of course no one is required to provide it.
It's pretty easy to justify why you would lie, if I think you are an ideologue who truly believes that Facebook trending topics must be curated with a certain slant for the greater good.
When you believe in a conspiracy theory, hearing "why would I lie" doesn't change your mind, quite the opposite. It's also not true that there's "nothing that anyone can say that would prove that any system works as described". There's no general statement that will convince everyone, because everyone has personalized doubt about it.
It's certainly possible to assuage the fears of a conspiracy theorist - take their examples, give a credible, particularized explanation(not a vague "it's algorithmic", but describe the steps in detail), and show some goodwill to address their underlying fears. What you perhaps wanted to say was that you don't really care about convincing conspiracy theorists, which is fine, but very different.
I believe you, I just think that the thing you made is not really minor.
It has incredible reach and is quite effective in claiming attention. I actually had to use uBlock's element hiding function to keep myself from reflexively looking at it and reading a bunch of news stories. I would be surprised if that wasn't true for many people, as that's what it was designed to do.
I guess asking for proof is an unreasonable thing in this case as I can't think of what would actually constitute proof. I do think that additional questions are reasonable in this case as the editorial control of the ranking is currently a topic of national interest. I'm not really sure what that means exactly in this conversation, but I have a vague feeling that things that are big should be examined more closely. That's not super fair to facebook compared with a traditional media company, but this thing is new and isn't really like our models of how media companies like newspapers and magazines work.
It's a little scary because of the power a couple headlines sprinkled here and there have when they're seen be a lot of people. Something that was nothing becomes a scandal, lies become truths in the public consciousness and can't be fixed (look at the antivax movement). Of course, they also have the power to do great justice as well.
I guess, my point after all this text is still that what you've built isn't minor, there will be and probably have been real world impacts from it. Those impacts stem from public trust in FB's editorial position. If the public doesn't trust FB to show unbiased stories, they interpret the state of the world vastly differently than if they trust FB. This is why I think it's reasonable to have questions, even if they may be somewhat pointed at times.
That said, I really appreciate the fact that you took the time to respond to this thread. Talking to the people directly involved is a great way to disabuse one of falsehoods. :)
EDIT:
For an example of a reason why people are interested in this capability, imagine a rouge FB employee were to push the following headline to everyone: "US Nuclear Arsenal Almost Fired at Russian City"
The world would see this post made by one person, and the fact that it was pulled nearly immediately would be seen as evidence by some of a cover up and could add tension and possibly instigate an international incident. Until this generation died, you would have people all over the world that would believe that the US nearly nuked a Russian city without provocation.
I don't think Zuckerberg is gonna call you and verify his employment.