I don't see anything controversial with Luke force choking the gamorreans. Technically force chocking is not a dark side power. Yes it is often used by darksiders and not by jedi, but that does not make the act inherently evil. After all it is an example of using Telekinesis (http://starwars.wikia.com/wiki/Telekinesis), something users of both sides can use. It depends on how certain Telekinesis is used, in whether it is darkside or lightside. For example, if a force user uses force push to intentionally push a man to his death, even though it wasn't in self-defense (but murder) while taking pleasure in doing so, then that is pretty darkside. That doesn't mean using force push is evil because darksiders can use it for evil, for a Jedi can use the same technique for non-evil purposes. Now if Luke chocked the Gamorreans, and though they were no longer a threat, preceded to chock them to death (while feeling negative emotions) then yes that would be a step towards the darkside. But no, Luke force chocked in a more good way, just using it to stop the Gamorreans from preventing him into the Palace, but not using it to kill (he let them go after he passed).