From a moral standpoint I fully agree with you. I just want to know if there are any specific Halachic justifications for this and their sources

Almost the entire book of Shoftim is based on this principle, where Ehud, Gidon, Yiftach, Shimshon (e.g. 16, 28) et al all went to war to retaliate against the enemies of Israel in defense of Am Yisrael in Eretz Yisrael. See also the Rambam, Hil. M'lachim u'Milchamoteihem, ch. 5-7. In those battles, fought on the battle-field, inevitably less civilians were harmed, because normal people (unlike Hamas terrorists) don't use their wives and children as human shields. Accordingly, they were usually taken captive, as was the custom at the time (e.g. Chronicles I, 5, 20-22; and II, 28, 6-8. For a comprehensive study with many sources, see the article on the topic by Rabbi Prof. Neria Gutel, at: https://www.zomet.org.il/?CategoryID=266&ArticleID=265