Why shri ram let the vanaras burnt the city of Lanka. My question arises because when Shri Ram and vanara get healed by sanjeevni and decided to continue battle, Sugriv ordered hanuman and other vanaras to set ablaze the city of Lanka. Many non-combatants died. As described in whole in this whole sarga: http://valmikiramayan.pcriot.com/utf8/yuddha/sarga75/yuddha_75_frame.htm
But during fight with Indrajeet when lakshman decided to use brahmastra which was capable of destroying not only Indrajeet but also whole race of demon, shri ram refrain lakshman from using it and said as:
तमुवाच ततो रामो लक्ष्मणं शुभलक्षणम् | नैकस्य हेतो रक्षांसि पृथिव्यां हन्तुमर्हसि ||
Then, Rama spoke to that Lakshmana, who was endowed with auspicious bodily marks as follows: "You ought not to kill all the demons on earth, merely for the sake of a single demon."
अयुध्यमानं प्रच्छन्नं प्राञ्जलिं शरणागतम् | पलायन्तं प्रमत्तं वा न त्वं हन्तुमिहार्हसि ||
You ought not to kill on this earth one who is not fighting or one who is hiding or one who seeks refuge with joined palms or is fleeing or is intoxicated.
Shri ram clearly says you should not kill one who is not fighting with you, then why he let vanaras burn the city, which will result in death of non-combatants.