I am very glad 4E avoids these complications by not forcing paladins to be Lawful Good - which lets the DM set up his world as he pleases.
To be clear, I actually like having Holy Knights for all alignments- "Paladin" being the most common nomenclature for the LG version- which is one reason why I absolutely love Book of the Righteous.
But IMHO,
all Holy Knights should have certain things in common.
1) Unlike a Cleric or Druid who may find his or her way into the holy man biz by a number of routes, a Holy Knight should experience "The Call."
2) There should be some kind of Code by which they live- the CN or CE ones, too- even though it may be quite simple. The CE Holy Knight ("Hunter-Killer?") might have a Code by which he must never let a day pass without performing an Evil act, unless he seeks to spread Chaos & confusion.
That could be as simple as confusing foes by performing a rescue of innocents, allaying fears that he may be Evil by performing an act that is, at its surface, Good. If he has any doubt about losing his powers by dealing in that kind of deception, he should put the innocents in jeopardy to start off with...all the better to be in position to be the "hero" who makes the rescue.
3) Failure to abide by the strictures of the Code leads to a loss of power.
I could see, for instance, a CE Holy Knight losing his powers until he
Attones if he rescued a bunch of children from a fire (esp. one
he set), assuming it was a genuinely altruistic act and not merely a ploy to win the confidence of the people rescued (and their families).
The Divine has a mission, a plan for the Holy Knight PC...and the HK is on a short leash.