Generally speaking, lots of societies chose to survive by raiding. In many cases, they were paid to either fight for other societies or bribed into leaving others alone, but it Is a survival strategy. For that alone, you'd have reason for feeling bad for killing what amounts to people surviving.
Until, you know, you get to the whole torture, mutilation, enjoying murder for the sake of murder...
I recall sneaking into one raider camp and taking a few minutes to let a couple of raiders share a story. I was going to let them live... up until they laughed at the punchline of burning/drowning their new friend to death for the lulz.