This has nothing to do with free speech. Just like when you go to a publisher and they tell you they won't print your book. You can still print the book yourself or somewhere else and this is exactly the same situation with things on facebook, twitter or reddit (on reddit you can even just go to another subreddit with different moderators).
So this is not a free speech issue, but an issue that websites like facebook twitter and reddit have lots of power that they could abuse. They actually don't look like they're abusing it, but are sometimes a bit overcautious in removing stuff that's not supposed to be endorsed.