Make it the 100th such act, then!
So, 100 times, the Paladin has been faced with the choice of either saving his mother or failing to prevent the certain destruction of the world at the hands of the Forces of Evil? Seems like the other 99 didn’t pan out quite as expected, did they?
If he does not immediately lose his Paladinhood, then do we now accept the act in question was not Evil? OK, so what is our justification for removal of his Paladinhood? Has he committed 100 non-lawful acts in a row, or 100 out of 10,000? You are tossing out some mathematical number with no context whatsoever, which leaves no answer.
It’s not a spreadsheet. The Paladin does not compute that, if he rescues his mother, there is an 80% chance he can still shut down the Gate and prevent harm befalling anyone, a 10% chance that there will be 1-6 deaths (3.5 on average = 0.35 deaths), a 5% chance there will be 1-10 deaths (5.5 on average = 0.275 deaths) and a 5% chance that 2-16 people will die (9 on average = 0.45 deaths) which totals 1.075 statistical deaths which is more than 1 so saving his mother is not the greatest good for the greatest number (oh wait, we need to factor in alignment of those we will save – if some are not innocent, that throws the figures out again). He makes the call that certain death for one person is, or is not, an acceptable loss weighed against the risks from the delay in dealing with the Gate. Is Heroism sacrificing the few to save the many (well, tear out that baby’s throat, I guess) or is it finding a way (or striving to find a way) to save them all?
If the paladin/cleric serves a cosmological force of good, and loses abilities for it, how can s/he refuse to acknowledge that s/he acted evilly? I don't understand the reasoning process that would make sense within that campaign framework.
The Paladin does not have a Player’s Handbook to tell him what circumstances cause a Paladin to be judged, nor does he get an explanation from the GM. He has to make his own calls. Perhaps he acknowledges he made an error. Perhaps he has decided that the Gods of Good are unwilling to make the hard choices – it’s easy for them, up in their Heavens – they are not down here in the fray. Maybe he has drifted from their “perfect good in an academic sense in their ivory tower” to a belief that compromises are a necessary evil here in the real world.
I don't know of any real-world doctrine of enlightenment that holds that complying with the ideals of enlightenment will itself render you, per se, enlightened.
You keep shifting between Real World and Fantasy Game. We were discussing those PC’s who serve beings of perfect enlightenment. You have indicated none but the player may judge that his character has strayed in any way from the tenets of his beliefs, and the wishes of the force he serves. So if the player says the character never strays, then the character must be behaving in the manner of one who is perfectly enlightened. How can he do so, if he himself is not fully enlightened?
If the requirements of LG are settled, then choosing to do something different is choosing to do something that is not LG. If it causes you to immediately lose your paladinhood, that is sufficient proof that it is evil.
Have you lost Paladinhood for straying from Good (you have become LN), straying from Law (you have become NG) or for committing a single Evil act? How do you know?
A paladin who nevertheless insists that s/he made the right choice is therefore asserting that it is good to do evil. On any non-ironic use of either "good" or "evil" that assertion is contradictory, given the premise that good has been objecitvely defined by those cosmological forces.
Or perhaps he has decided LG is not the ultimate Good. Perhaps LG sacrifices too much Order to individual rights. Perhaps it is too willing to allow a few to suffer for the good of the many. Or perhaps he has come to realize (believe) that the standard set by the powers of LG is one that cannot rationally be attained in the real world, only in their paradise where the forces of Evil and Chaos are far, far away and don’t really need to be opposed.
As I said above, in the real world people can reject the condemnation of someone who claims to be good, while still affiriming their own goodness, because they can reasonably deny that some judging agents has a true grasp of objective moral requirements. But if the campaign starts from a presumption that there are objective cosmological forces who do have such a grasp, there seems to be no scope for such denial.
And denying the rightness of a paragon of Lawful Good seems, to me, to deny that Lawful Good is the best alignment – perhaps LN or NG is the best alignment, and those LG’s have it all wrong. The followers of each alignment believe their way is best. To accept your position that one is clearly right requires me to also accept that all the others are clearly wrong. I do not accept that.