The SS was, generally, a volunteer thing; they did not conscript for the SS proper. The Wehrmacht was, at least by the period we're concerned with here, a conscript army, but the SS wasn't.
Not to defend any particular case but I think it is easy to see that there must have been a time when the volunteers had no idea what they were in for, and that after they were in too deep they might have feared for their lives. Many of them probably had no idea what atrocities were going on in the name of their country. So, I think you need to judge people on a case-by-case basis when it comes to alleged war crimes. The same goes for people who join political parties in countries where it is a virtual prerequisite to any kind of professional work. Not only may they be unaware of the bad deeds of the party, but they may have concluded that they could do nothing about the party's actions anyway.
He didn't just volunteer; he volunteered for the SS-TV. Read up about what that unit was about. He had opportunities to stop what he was doing; he didn't take them.
There was never a time when people had to fear for their life for not wanting to work at a concentration camp. It was a volunteer assignment. Transferring to a different assignment would lead to a loss of status, but not serious punishment.
