I am assuming collateral damage includes only humans or human-like living forms like vAnaras, rAkshasas (and does not include animals).
There is an episode in the vAlmiki rAmAyaNa which throws light on this question. When Indrajit was tormenting the vAnara sena along with rAma and lakshmaNa by (ab)using his ability to become invisible during battle, lakshmaNa wanted to put an end to the entire rAkshasa race by using brahmAstra. But rAma disapproves of it because it is against dharma.
लक्ष्मणस्तु सुसङ्क्रुद्धो भ्रातरं वाक्यमब्रवीत् |
ब्राह्ममस्त्रं प्रयोक्ष्यामि वधार्थं सर्वरक्षसाम् || ६-८०-३७
- tataH = then; lakShmaNastu = Lakshmana for his part; kruddhaH = was enraged; abraviit = and spoke; vaakyam = the following words; bhraataram = to his brother; prayokShyaami = I will employ; braahmam astram = the missile presided over by Brahama; vadhaartham = for the purpose of killing; sarva raakShasaam = all the demons.
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.
तमुवाच ततो रामो लक्ष्मणं शुभलक्षणम् |
नैकस्य हेतो रक्षांसि पृथिव्यां हन्तुमर्हसि || ६-८०-३८
- tataH = then; raamaH = Rama; uvaacha = spoke; tam lakShmaNam = to that Lakshmana; shubhalakShaNam = who was endowed with auspicious bodily marks; (as follows); na arhasi = you ought not; hantum = to kill; rakShaamsi = all the demons; pR^ithivyaam = on the earth; ekasya hetoH = for the sake of a single demons.
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 || ६-८०-३९
- tvam na arhasi = you ought not; hantum = to kill; iha = here; ayudhyamaanam = one who is not fighting; prachchhannam = or one who is hiding; praaN^jalim = or the one who is a refugee; palaayamaanam = or who is fleeing; mattam vaa = or who is intoxicated.
"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."
अस्यैव तु वधे यत्नं करिष्यावो महाबल |
आदेक्ष्यावो महावेगानस्त्रानाशीविषोपमान् || ६-८०-४०
- mahaabhuja = O long-armed Lakshmana; yatnam kariShyaavaH = we shall try; vadhe = to kill; tasyaiva = only Indrajit; aadekShyaavaH = we will employ; astraan = mystic missiles; mahaavegaan = with great impetuosity; aashiiviShopamaam = and which are equal to venomous serpents.
"O long-armed Lakshmana! We shall try to kill Indrajit alone. We will employ mystic mssiles with great impetuosity and which are equal to venomous serpents."