The difference would be for the deplorable, who now has no "mah free speech" and "reddit is censoring me!!11!!" excuses to fall on and justify its deplorability.

More seriously though, the important thing about ActivityPub is that it removes central points of control. No matter how much you agree/disagree with the governance of Reddit/Facebook/Twitter et caterva, they are just too big for the good of society. Federated systems is one chance to take this power from them and bring to people - if not directly (say, because you don't want the pain of hosting/managing all that crap) at least you can delegate this power to someone closer to you - or at very least to a bigger number of smaller providers who will them have no monopoly and will have to keep your interests first.