Imagine an all-volunteer orchestra where everyone is free to play their own tune. Even without a strict conductor, the orchestra members are aware that their individual performances affect the harmony of the entire group. If someone plays discordantly or off-key intentionally, they might not be solely responsible for how the audience feels about the music, but they do contribute to the overall experience.
When members of the orchestra (or posters on the fediverse) disregard the collective effort to create something enjoyable and cohesive, they risk being “downvoted” to the last chair, where their impact is lessened. However, their presence and performance can still affect the overall sound. So, while you can say what you want, your words are part of a larger community conversation and can influence the “melody” of the platform, for better or worse.