I expect people rooting for Seven to murder the unarmed bad guy because its practical should also root for that grieving mom in Silicon Avatar to destroy the Crystalline Entity.
I root for her. I think she was right and Picard was wrong.
This one is tough. How aware of what it was doing was the crystalline entity? Was the entity aware that it was consuming sentient beings or was it just feeding as we all must? We'll never know because dr. Marr destroyed it before we could get those answers.
Should have the human scientists in Home Soil (the "ugly bags of mostly water") been destroyed for their inadvertent transgressions?
How about the civilian miners at Janus VI? They didn't know that they were destroying Horta eggs.
How about Paul Stubbs? The nanites would have been within their rights to exact lethal revenge, but they chose not to. Hell, I wouldn't have argued with them.
None of these people were fully aware of the consequences of their actions on others, and thus were forgiven.
Bjayzel was fully aware of what she was doing. She was a serial predator, knowingly harvesting living beings, not for survival, but for profit. A criminal. Furthermore, she lived in a sector of space where legal action, judgment and imprisonment was impossible, and was therefore immune to any legal reprisals. Furthermore, she may have been unarmed, but she had a legion of armed thugs at her disposal that were in the next room. Virtually untouchable. Given all of this, how else should Seven have dealt with Bjayzel? Should she have taken her into custody? And turn her over to who? She's committed no crimes in Federation space. There's no legal justice system structure in the former neutral zone where Freecloud is located to turn her over to. What were her options? Say, "oh well the courts can't touch her so I should continue to let her harvest XB's"?
If they were to give Seven of Nine and her Rangers a spin-off, what I would like to see them do is, not to get that sector of space in line with Federation doctrine, but to establish their own seat of government to bring order to the region.