Although reddit acted as a free speech haven for a long time, it was only overall, and not ever in major specific communities. True free speech is valued because it fosters debate, and allows bad speech to be rebutted by more speech. A marketplace of ideas, and maybe more importantly, the counterspeech doctrine, are incredibly important principals in justifying the existence of free speech. Fiefdoms more often than not were echo chambers, where to see a response to bad speech, a person would have to know where else to venture. By creating filter bubbles, tribes, echo chambers, reddit was not an exemplar of a free speech haven, but instead a collection of lopsided megaphones pointed in opposite directions, strewn across a hard to navigate map.
Strong moderation is what allows communities with strict quality guidelines to function, but also amplifies division.
And on the topic of history, a part of me finds it unfortunate that this banning will make historical, sociological, and psychological analysis of trends, thoughts of the times, past bad behavior etc much harder. It's no what.cd or house of wisdom or library of alexandria loss, but it is still a historical record loss of a huge event that happened. I may not have personally liked The_Donald but it was quite the experience, as a fish out of water, to go look at how other people think, communicate, and reason. The culture that developed there will continue to exist, but the ease with which one could passively observe it, and learn lessons from it is greatly diminished. Another double edged sword.