...yes, if the ends justify the means. If it were in self-protection or in protection of my family, then yeah, definitely. If someone had deliberately caused a severe amount of suffering to someone I love, or maybe even someone I don't know, I would gladly purge their existance off of this planet. Similarly, if I know someone has used their life to committing acts of evil (and it was my job to hunt them down) I would do so without a second thought.
In a blackmail "your life or that innocent bystander" situation where the person ordering me to kill is out of my reach then yes, I suppose I would do it and then feel a horrible sense of guilt about it. Maybe I'll get over it, maybe I won't, I suppose thats my atonement.
Finally, if OP just meant kill someone randomly, then no. Definitely not.