Given the huge emphasis in 5e on making the game what you want it to be, I don't think this argument holds water. I'm willing to bet that, either in the PH or the DMG, we'll have a sidebar on paladins losing their powers by violating their code in some campaigns. Or maybe it will be in the main text for the class. But I'd bet $5 that it's going to be mentioned in there somewhere.
And really, even if it isn't, this is such a simple thing to keep in your home game that I don't see any problem at all.
Show me the sidebar in the DMG where not murdering defensely kobold children with Divine Smite despite your paladin's vow of Justice prohibiting killing the weak, has a mechanical impact, and we'll talk.
Until then, in 5th ed, one needs to houserule good = good, because otherwise evil = good or whatever else you get away with.
I've seen several selfish murder hobo paladins in Encounters. Having no rule to support your vows is akin to giving players free reign to demand that for RAW-aligned DMs, there is no such thing as good and evil, lawful or chaotic, because even if there were, there is no mechanical repercussion for a paladin acting CE despite having LG on his sheet. There isn't even a way for a DM to alter alignment based on their character's actions. That is totally absurd and ridiculous. Alignment is a mere suggestion, of course, because the designers have decided that morality doesn't actually exist. That's a strong statement and one shared by many intellectuals. If so, why have alignment at all? Why have Oaths if you can violate them willy nilly? Why design a class based on receiving different abilties based on a divine oath or other, when there is zero reason for a character to actually follow that Oath? I could play an Oath of Vengeance paladin, who is un-vengeful in the extreme. Is that good roleplaying? Is ignoring the "flavor text" of 9/10th of the class description a good reason to spend pages and pages and hours and hours designing it?
I submit to you that it's not only unreasonable to have a class based on Oaths without consequences for violating them, but it's completely unreasonable to have any form of alignment mentioned anywhere in the PHB if there is no mechanical support. It is just fluff. I don't need a PHB to tell me what good or evil is, what a lawful character is. If I did, I would want to know why I can pick a class that used to be based on having a certain alignment no longer requires an alignment, and what it means, if anything, to have taken an Oath of Whatever when there is "whatever" shoulder shrug response from the DM when your character is the most selfish and petty at the table. I've seen it quite a bit.
Paladin players are the trolls of D&D. They want those kewl abilities but no penalties for hitting below the belt. They want to swagger in to town as the hero on shining armor after having acquired their celestial mount as a result of murdering a bunch of defenseless captives who had surrendered. This is the kind of game they've created here.
I simply can't play a class that's so ill suited to D&D. You need mechanics for alignment if you build an alignment based class. Perhaps one for each alignment, fine, but there should be an LG paladin who loses his powers if he commits an evil act, in D&D.
I bet they won't even have that in the DMG as an option. It seems we have options for mages to fuel their spells in various ways, but paladins can't actually have their code of ethics be supported by the rules.
I'm not impressed by some munchkin who has a level 9 paladin that he got there by chasing loot and acting cowardly or selfishly. D&D Next is supposed to be supporting parties consisting of characters of various levels within the same group, so if there are two paladins, both LG on paper, and one plays him like a real scum bag, but the other plays him well, I expect one to advance faster than the other.
The only thing I find really surprising is that on a website dedicated to roleplaying, that the idea that good roleplaying would be rewarded in the rules and bad roleplaying penalized, is the least bit controversial. Games have reward conditions for playing them well and fail conditions for playing them badly. A roleplaying game with no rewards or penalties for good/bad roleplaying is simply poorly designed.
The original D&D was exquisitely designed compared to some of this modern stuff. By the time the DMG comes out, I won't be surprised if there's just a sidebar for atonement, or even none, because of all the murder hobo / moral relativism the designers read about on the forums. D&D without alignment is less D&D than it should be, it's missing its heart and soul. Paladin atonement being present or absent, I've noticed is a fair indicator of what type of players will play the game, and as a result, what kind of tables where I will inevitably be seated with greedy paladin murder hobos where the DM can't sanction them directly via their god because they are prohibited by organized play rules to roleplay the paladin's god effectively. The quickest and simplest way for deity to sanction their errant knights is to ex-communicate them, or keep the ever-present threat of ex-communication looming over their every move. In practice, this is how real morality often plays out. And in the end, I don't really care if a paladin acts good because they are inherently good or because they are obeying their deity's dictates, what I care about is that I'm not stuck in a group with a sadistic murderer in shining armor who absurdly gets rewarded with such supernatural and divine abilities like "detect evil" or laying on hands (when the last 5 times it was used was to sustain some kind of evil act or its aftermath).
