Free Speech does mean what you describe it not as. But there is no legal body to punish you for violating the principle. It is similar to 'primum non nocere', translated roughly to 'do no harm', extremely common in medicine and something you may see alongside the 'Hippocratic Oath'. You can be in violation of that principle or the oath at any time, some people even get fired for violating either as a pretext to malpractice. Some even argue that it is quite impossible to abide by this principle, and yet, it is something many people take on as responsibility everyday all across the globe.
I won't argue about websites and their rules, they have their own set of principles and violate plenty of others, sometimes they even violate their own principles. But Free Speech is not just the law and interactions one may have with their government.
The twitter retweet constantly amplifies and the tweets are centered around an account vs a post.
Reddit should behave similarly but I think subreddit topics stick longer.
Of course, that also soft-forces everyone to move on. Once a thread is a day or two old, you can still reply, but the person you've replied to will probably not read it.
This drastically increases time between messages on a topic, lets people cool off, and lets a topic naturally die down.