Moderation is necessary for a conversation involving many people. Regulation is necessary for markets involving many competing interests. Even in families, even in 1 on 1 relationships, there are rules. So there always are laws, guiidelines, rules, etc.

Having the rules in writing in my opinion is far superior than having then unwritten. Unwritten rules get enforced just as hard if not harder than the written rules. Unwritten laws also don't even give you the chance to learn what the rules are which you are being judged by. In essence you don't know the rules until you break it.

Considering that you cannot know how someone will react to something you say before you say it, if you have too few constraints on what you can say then your chance of upsetting a bunch of people rises. So how would you solve this without adding constraints and in effect reducing some liberty?

It's not ideal at all, but it's about maintaining harmony, quality of life, and preventing "mob justice" from being the ultimate arbitrator of disputes.