Is it about paladins, or alignment?
Since this is a 4e thread, and paladins don't have obstructive codes of conduct anymore, this is less of an issue than in other editions. If the paladin player is being disruptive, tell them to stop (out of game), or they have to create a new character. If they stop being disruptive and switch their alignment, they will still be a paladin, as their powers cannot be taken away once they've been ordained. (If it's 3e, you've got another problem. Write a new code of conduct that's designed for a playable game and not a pre-written novel. Don't look at old ones, and make sure it's clear. I've literally never seen a clear paladin code, even when people on this forum created threads specifically for creating sane codes.)
Alignments were supposed to be guidelines, but for many players and DMs they haven't worked out that way.
My first edition was 2nd Edition, and it was punitive. They gave an example of a player switching from neutral good to lawful good (or rather, they wrote NG on their sheet but the DM interpreted their behavior as LG), and in the example the DM didn't tell the player about their "concerns" beforehand, but simply said they're now LG. So? Well, switching alignments cost you XP! A player's character was mechanically punished for an RP issue, and the player was in no way being disruptive or a bad influence. (At least this is my recollection, but that was more than a decade ago.)
It didn't help that alignments were never clearly explained (TVTropes does a better job than TSR or WotC ever did; at least if I disagree with TVTropes their explanations are clearly laid out so I can clearly state my disagreements), which only makes things worse when the DM and player don't agree on a PC's alignment. The DM always wins an argument, and at least in earlier editions this could cost anyone XP. In later editions, your paladin could fall, your cleric could be forced to switch religions (and abilities like what you could spontaneously cast), your druid might have to give up all their druid abilities, your bard, monk or barbarian might lose the ability to gain levels in that class, etc, and this is on top of the "alignment blast" spells and aligned weapons (the higher level spells were broken even without taking alignment into consideration).
Finally 4e severed the connection between alignment and rules. They also simplified the alignment system (eg there's never been a good explanation of what chaotic neutral or lawful evil meant, so they're gone), which naturally drew heat.
Apparently some campaigns have managed to make alignments important, not too restrictive, and "good" (for lack of a better word) but trying to get people to agree on alignments seems, to me, to be more trouble than it's worth.