The line is from Hamlet--I forget the act and scene, but it's Laertes. Claudius has asked the young man what he would do to avenge his father, and this is Laertes's answer.
Pretty hardcore, right? You gotta admire a young man with convictions.
And also, contrasted to Hamlet's actual actions, both far more humane, and far less humane.
See, Hamlet, as you may remember, had been in a similar situation earlier on in the play. He was hiding in the confessional when Claudius came in and confessed, with tears and true repentance, that he'd actually killed Hamlet's father.
Hamlet had the perfect opportunity to kill Claudius--he was right there.
But Hamlet claimed that he didn't want to kill Claudius there, because he'd just confessed his sins and he'd be good to go. I mean, getting struck from lightning when you're exiting confessional is both a big f-you from God and a huge blessing in disguise. Unless you're schtupping someone inside the church you're going to heaven with a clean slate, do not pass purgatory, go straight on up, right? At least according to the Elizabethans, and those people had their heavenly ascension down to a science. (Literally. They had a heavenly ascension chart the same way we have a periodic table. For real.)
So, on that point, not killing Claudius was really the least humane way to go.
But I've always maintained that it was also the action of a just man who refused to--hey!--cut a praying man's throat in a church.
Of course some of the irony here is that Claudius really felt like he couldn't pray, because he wasn't giving up any of the good shit he'd gotten from the murder, but Hamlet didn't know that--he was assuming that Claudius had no conscience and that the confession was the be all and end all of the justice.
So which way was "better"? Which action was the bravest, the noblest, the most manly and kind?
Well, let's look at what would have happened if either one of them had changed their course of action.
If Hamlet had killed Claudius in that church, Ophelia would have lived. She'd already betrayed him, but he might have forgiven that, and hey, he wouldn't have Polonius's blood on his hands. (I maintain Polonius was not as innocent as some portray him, but that's another chat.) HIs mother would still be alive, but she'd hate him, and he either would have had to flee the country forever, or been hanged as a murderer. Either way, he wouldn't have gotten to taste the sweet breath of freedom as he betrayed his two childhood friends who were only following their king's orders (I'm bitter about Rosencrantz and Guildenstern, so sue me) but he also might not have gotten to taste the sweet sincere love of a good man who was not passion's slave. (That last part is pure speculation on my part, but only because I ship Hamlatio with a nerd's zeal.)
At the end of the play, everyone would be alive except Claudius, but Denmark would be fucked and Hamlet's life in shambles.
Let's see if Hamlet did kill Claudius, but Laertes, one of Hamlet's most prominent foils, decides to take the same route and not execute perfidious revenge.
Well, Polonius would still be dead, and so would Ophelia, and that would suck, because seriously, poor Ophelia--I think Hamlet loved her, but in the end she was only a tool. *shakes feminist fist in true anger* But in the end, everyone else would live. Hamlet has forgiven Claudius, forgiven his mother, and he and Horatio might live in "Fuck you, I"m over Denmark" bliss for many years to come. Hell, Laertes could come with them. They would be a threesome and I could write that ship a thousand times, huzzah!
But notice what doesn't happen with either of these scenarios--
Claudius is never revealed.
Gertrude never shows her son that she loves him more than she loves Claudius.
Hamlet hasn't grown into the person who could, with such understated philosophy, accept that death would come or it would not, but he would live his life with serenity.
Laertes would never have grown beyond his father's shadow to the point that he could recognize the evil in an authority figure whom he'd been trained to suck up to until the last sip of toe sweat.
Denmark never gets the sublimely manly and commanding leadership of Fortinbras upon her throne to fix the entire goat-fucking cluster-hump that was Denmark's political family.
Hamlet's father is never avenged publicly.
And, of course, Horatio and Fortinbras are never allowed to unite in coital bliss. (Look, if Hamlet's dead, Horatio still has to bang somebody. It's my ship, dammit!)
Extremism rarely solves anything, and knowing when to act and when to stay your hand is an incredibly tricky business.
If you look at the end scenario, Hamlet met his end with a clean conscience and most of his to-do list checked off, and he got to do that because he walked away from an amoral act.
Laertes's actions provoked the end of his family name and the end of Denmark's monarchy, all in one rash vow of vengeance.
Of the two young men, the one who did the most overtly humane thing ended up in the best shape as the last breath was drawn.
Hamlet is a deeply flawed play--I took a master's course in it. I mean, I've had nearly 18 units of Shakespeare, and this fucking play figured large in more than a semester's worth of analyzation, and one of the best and worst things about it is that there ARE no cut and dried answers. If you're reading MacBeth or King Lear or Othello, you KNOW what you want the hero to do and who you want dead at the end.
If you're reading Hamlet?
ehhhh... it's a crapshoot.
But then, real life is like that too.
I just refuse to believe that cutting a man's throat in a church ever led to anything good.