Since I don't have any insight into their algorithm I'm going to use a naive hypothetical example: Say they did have a system to downrank negative/harmful/spammy content and it works by applying some kind of embedding model to posts and comparing their cosine similarity to a dictionary of known bad content. You have the code, but neither the trained model for doing embeddings nor the set of "bad" vectors. Can you answer the question: Is it politically rigged?

That's why I tend to be in agreement with the idea of treating it as a black box and observing what biases it exhibits.