I'd have felt bad for them if it wasn't for some contradictory aspects of their behaviors that cannot be excused as "being forced", like Annie yoyoing a Survey Corps member, or Bertolt choosing to kill Armin in a very horrible manner instead of doing it quickly and painlessly. What they did was completely unnecessary and uninstructed, and none of them felt any remorse after the acts and just left their victims aside to continue with their murder sprees.
This is not how an innocent person who is being forced to do things against their will behaves, but it reveals a truly sadistic part of their beings. Bertolt's personality transformation during the Battle of Shiganshina seemed to have morphed him into an actual psychopath. Many criminals are born in the same fashion, and the situation had reached a point where they weren't going to stop and had to be eliminated for the good of the societies they meant to harm.
In the specific case of Bertolt, it seemed fitting to be killed by the person he had tried to kill [twice], and who he had also tortured savagely and left for dead. You can hardly find a better example of anything resembling the concept of "karma".
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