Difference between Sri Rama and Indrajit

During the battle, Sri Rama and Lakshmana take their bows to fighting. Gates and buildings in the city are tumbled down by Sri Rama's arrows. 

Ravana instructed Indrajit his son to proceed to the battle-field. Offering oblations in fire and gratifying the gods, the devils and demons, Indrajit ascended an excellent and splendid chariot, capable of disappearing from sight. 

Protected by the missile presided over by Brahma, Indrajit became difficult to be attacked, and vanished from the sight.

Indrajit came to the battle-field and saw the two brothers, showering a multitude of arrows. Indrajit with his chariot, reaching the sky and remaining invisible, struck Sri Rama and Lakshmana with his sharp arrows.

No one could perceive his rapid movement, nor his form nor his bows and arrows, nor any other thing about him whatsoever could be known. Struck down by him, many Vanaras were killed. 

Then, Lakshmana for his part was enraged and told his brother that he would employ the missile presided over by Brahma for the purpose of killing all the demons.

Then, Sri Rama stopped him saying he should not to kill all the demons on earth, merely for the sake of a single demon.  

Indrajit had enimity towards Sri Rama and Lakshmana only, but earlier Indrajit employed Brahmastra by which Sixty seven crores of Vanaras were struck down.  

सप्तषष्टिर्हताः कोट्यो वानराणां तरस्विनाम् |
अह्नः पञ्चमशेषेण वल्लभेन स्वयम्भुवः || (Yuddha Kanda 74 Sarga 12 Sloka)

Sixty seven crores of powerful monkeys were struck down by the cherished missile of Brahma, the self-born creator, in the fifth and last period of the day.

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(The twelve hours of the day were commonly divided into five parts consisting of six Ghatikas (or two hours and twenty four minutes) each. They were known by the names of PraataH (early morning), Sangava (forenoon), Madhyaahva (midday), Aparaahna (afternoon) and Saayaahna (evening))

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However, Sri Rama did not want to employ Brahmastra on the entire Demon race, for eliminating a single demon, who was fighting by remaining invisible. 

That was the greatness of Sri Rama, who was stickler to Dharma.