The thing she refers to must have happened after his maniacal ascent, it is evident he never killed anyone before the TPS events. When we meet Jack in TPS, he’s an underling sucking up to his superior. And that Angel was dangerous and accidentely killed her mother (and Jacks wife) is a common knowledge, and also a reason why Jack decided to contain her power and prevent her from hurting anyone else or herself.
Before he became a full-scope villain in BL2, he was a sort of anti-hero. And one of the points of the Helios laser was indeed to destroy entire towns. With no freidnly casualties. You know, because 99% of Pandora’s population are bandits and crazed psychos which attack you on sight, and main heroes of BL1 and BL2 wiped entire towns of them, just on foot and with regular weapons/powers.
The artifact he was using only contained knowledge, and the knowledge was being poured into Jack, so no point in just destroying artifact. Lilith should have killed him right there. Instead she scarred him both physically and mentally, gave birth to a person who killed her beloved one (funny thing, in mythology “Lilith” is a name of a mother of demons). Karma.
Everything he did before going full Handsome Jack was for the greater good. He wasn’t selfless that’s all. It’s not a regular good guy who just wants to save the world, it’s the guy who wants to save the world and have something to show for it afterwards. It seems more human to me. Good for the sake of good is too boring. And his approach was actually practical, and the way most modern military superiors would operate.