Not all of them were. I acknowledge that some of them were, if fact I've gone on length about how the exploitation of a lot of the younger people is one of the darker themes I'm fond of in a
blog post I did recently, but that gives even less of a reason for Hamazura to be espousing the Dark Side was necessary for them.
There's a difference between having a place to belong and that place being the cesspit where he had to dispose of bodies of victims who will continue to be missing or have been erased while their loved ones remain clueless. That isn't Skill Out territory (which isn't technically a part of the Dark Side) and that's not even the darkest depths we're talking about here. Accelerator's goal is to bring all of this to light so that they get their shot of getting out of the cesspit.
That's why I'm all for them getting taken in by Anti-Skill so they can give their testimonies and the ones who were pressed at gunpoint can at least get a shot at amnesty. They were victims too. The fact that they're being killed is the problem because if even those who were forcibly recruited are killed then the ones at the top are not only going to get away but that's more needless lives lost. But you can't deny that a lot of them took great pleasure in killing and didn't really feel remorse or pressure for it, even in the first volume that High-End Level 4 was gungho on offing people and outright asked why they couldn't just kill Last Order.
When Accelerator acknowledged his fall into villainy and doesn't give himself a free pass even when he's sitting at the top now, he set the standard for what needs to be done.
Which is part of what makes me mad that this is happening, someone is actively undermining his efforts to make AC a better place.