There's no problem with FSF or Stallman being discussed on HN. All that is on topic in principle. What's not on topic is endless repetition of a same-old flamewar.
When there's a major ongoing topic, one important test is whether there's SNI (Significant New Information) in a submission—or just a follow-up that's continuing the same discussion. If there's no SNI, chances are high that the discussion will be a repeat, and when the topic is highly polarized, you'll get a repeat of the same flamewar. That's what we really don't want here, so we downweight such follow-ups.
https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...
https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...
https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...
These principles are well-established on HN and have nothing specifically to do with Stallman, let alone whatever opinions the mods have or don't have. You'll see the same patterns about any major ongoing topic that's highly divisive. Assange stories, for example, are pretty much an exact parallel.
Your comment suggests you may feel like there's a bias in which opinions are being "allowed" - that's not the case. See my explanation above: https://news.ycombinator.com/item?id=26713636. It's all too easy to feel like the local authorities are biased against your view, but that perception is in the eye of the beholder—i.e. it's rooted in cognitive biases, such as the one where people notice the cases they dislike and overlook the others (https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...).