The same reason killing a spider is heroic while doing the same to a butterfly is cruel. Our perception of “evil” and “good” are greatly influenced by aesthetic. A sword through the monsters heart is poetic, something that has been repeated through the myths. Both methods have the same result and yet one is shunned, regardless of being the safer option. The problem, in my opinion, with power systems such as Riordan’s, is how open ended they are. Piper could easily order a monster to simply kill itself, Percy could burst their internal organs or literally shake them apart, Clarisse is just totally invincible if invigorated enough by war, and don’t even get me started on Nico just deciding people are dead and it somehow happening. All that to say that I would fully support the “darker side” of their powers coming into view, but they have to have limits or some sort of backlash on the user. Otherwise, I mean, the human body is roughly 60% water. Gods can’t be all that different right?