This is EXACTLY what Ecto tried to avoid.
Things were heating up within the group and he felt something needed to be done fast. He really didn't want to take any sides, this was never the plan.
He agreed that they shouldn't just stroke Wall Walker's hair, give him sugar cubes and send him on his way. He IS a bank robber, after all. And maybe... he felt like if Captain Powerhouse couldn't catch him, and he could, he would feel something... pride, satisfaction. He also kinda liked Graffiti, and didn't want to disappoint her.
But... murdering Walker in cold blood? That is insanely dark, stealing money does not deserve death. NOTHING should. A little pain? Maybe... but NOT death.
Getting into Walker's body seemed like the best idea at the time, since it was to harmlessly bind him in his place, and would also protect both of them from any trigger-happy ideas, thus, taking the middle ground. This way, they would have time to sort things out. At least, that's what Ecto thought...
He was shocked to see that Wraith didn't really think the same, and effortlessly pushed her hand right through Walker's ribcage. It was a sudden, cold sensation, her fingers, like icicles forming around his heart.
"Wraith, don't -" - then hell broke loose.
When Ditch kicked Graffiti's paintball gun out of her hands, Walker suddenly slipped from Ecto's grasp, like a smooth, silk blanket being pulled from you. Leaving Ecto where he stood, he suddenly turned around, and bashed Wraith in the face with incredible force. The girl staggered, her hand still in Ecto's body. "... keeping my hand insubstantial like this is an effort. As soon as I stop, well, that's when accidents become necessary, I'm afraid." - the words echoed in his head.
Oh no.
His side exploded with excruciating pain as Wraith's hand left him. To the outside world, it was quiet and mostly unnoticeable, like a gust of wind during spring, but for Ecto, it was agony incarnate. He fell to the ground, a thick liquid substance seeping from his side. Ectoplasm...?
When he managed to look up, the others were focused on following Walker, who had apparently taken Ditch with him in a tussle. Everyone rushed into the building after them: Omega, Raven Tale, Black Rose, Wraith... Even Graffiti. Did really no one notice him getting injured? Or they just didn't care...? He tried to center himself with all his strength, clenching his teeth.
"Sure... don't mind... me, just... bleeding to death. No biggie..."