If you you blow the guts out and faces off Russian soldiers by more traditional means they are just as dead

I (and all the people and organizations that have worked throughout the last century to get incendiary weapons banned as anti-personnel weapons) generally feel that the method of killing matters, and that some methods are excessively cruel or represent excessive risk of long term suffering.

The existing protocol on incendiary weapons recognizes the difference, by requiring signatory nations to go out of their way to avoid using incendiary weapons in places where civilian harm might occur. Even in contexts where a barrage of artillery near civilians might not violate the law, airborne flame throwers are forbidden. Because incendiary weapons are different, and a line is drawn there, knowing that there actually is a difference between negligently killing civilians with shrapnel versus negligently killing civilians with burning.

There are degrees of morality and ethics, even in war, and incendiary weapons intentionally targeting personnel crosses a line that I would draw.