Depending on the context of the community, such things can actually do more harm than good - many users react negatively to any display of authority, no matter how reasonable it is. I don't think community managers should have to subject themselves to the questioning of users who don't have anything better to do, if they don't feel like it adds to their community.
Of course, this does work in some places - Wikipedia is extremely transparent about its moderation actions and policies - but I don't think it should be the default for every single community.
I mean if the mods want to run their subreddit as a dictatorship that's allowed, and having a public log wouldn't stop that. It just means that you can't pretend you're not intervening if you are.
Yes and no. Like, is there a guy who decides who to kick out of the intramural softball league? Probably yes. But people will see that it's happened and talk about it, and if it was unreasonable then at some point they'll have a word with the guy, and maybe oust him or start their own splinter league or what have you. All of which is sort of possible on reddit up to a point, but those mechanisms are much less functional because the only community interaction is the subreddit itself where the moderator can just silently remove any posts they don't like.