Do you think it is right for some one to take the law into his/her own hands because some one has harmed this person? (This question is in reference to A Tale of Two Cities)

Wars and matters of national interest notwithstanding, it is morally wrong for a person or persons to seek revenge against others, especially when it involves taking human life. 
Madame Defarge knits the names of the enemies of the revolution, but it is because of her personal vendetta that she knits into her handiwork the name Evremonde. The Marquises Evremonde are both dead; they are the guilty ones. Charles Darnay, né Evremonde, has left France and never injured anyone. Furthermore, she has also recorded Dr. Manette in her list because he has pleaded for the life of Charles Evremonde (Darnay), the husband of his beloved daughter. 
When Monsieur DeFarge is troubled that Dr. Manette is on the list, he says to his wife,

"Extermination is a good doctrine, my wife...in general, I say nothing against it. But this Doctor has suffered much; you have seen him to-day; you have observed his face when the paper was read."

Angered and with contempt, Madame Defarge counters,

"Yes, I have observed his face! I have observed his face to be not the face of a true friend of the Republic." (Bk.3, Ch.12)

Madame Defarge would have Dr. Manette exterminated because he has allowed his daughter Lucie to marry Charles Darney, who is actually an Evremonde, the sworn enemies of Madame Defarge because the Evremonde twins raped her older sister and killed her sister, her sister's unborn child, her brother, and her father.