When I was young I didn't realize just how dark a past Aragorn actually has. While Tolkien never really delved into it, once he ventured out from Rivendell Aragorn spent many decades living in a very dark and brutal world. If you really stopped and thought about it Aragorn has probably done some pretty nasty things along the way. I wonder how many Bill Ferny's might be buried in shallow graves across Arnor. While it might be easy to say Aragorn's nobility and sense of honor might keep him from such actions it wouldn't surprise me to find out Aragorn and the Dunedain were brutal and merciless when the need called for it in protecting west of the Anduin or the Misty Mountains.
Considering Tolkien had originally planned to have Aragorn kill Boromir in single combat it wouldn't be too much of a stretch to imagine him having to take similar distasteful actions.
It speaks to Aragorn's strength of character that he could come through all he endured without too much damage.