When Blip had passed away, after finding out more information, Quinn had been made aware that there probably was something he could have done. There was time that had been wasted in between when Quinn had chosen to save the Parasite members, and getting back to the ship.
In truth, there was no way for him to know for sure whether or not he could have saved Blip's life that day.
Others had told him he had done the right thing, even Linda. She had great anger when she went to the Parasite's base. Quinn was questioning whether it was the right thing to do, but Sam had informed him she needed to see something.
She quickly realised that they too had families, children and others living there. When she felt like her brother's sacrifice had saved all these people, she felt a little better about it.
But for Quinn he felt different, he blamed himself for putting strangers' lives ahead of those he actually cared about, and this had happened more than once already.
