The Q Who and Emergence episodes from Star Trek: Next Generation explore the value of a sentient life. In Emergence, the Enterprise begins to form a “self-determining intelligence”. At first the Enterprise officers attempt to get rid of this intelligence, whose creation is threatening the crew mates. After this approach doesn’t work, they try to understanding it. The officers realize that inhibiting this new-found life-form from being born would essentially kill a sentient being, which runs contrary to the Enterprise mission of learning to understand different life forms even if that inconveniences you. The officers decide to help the Enterprise achieve the birth of the sentience.
Q Who shows a scarier type of life form: the Borg. The Borg look like thousands of biological bodies with an artificial intelligence and some artificial upgrades. However, they function more like the parts in a human body than individual beings; they are able to communicate instantly, work together seamlessly and adapt from the experience of the whole. The Borg make up one sentience. And the only thing the Borg really do is adapt technology from alien civilizations and destroy the civilizations.
On one hand, the Enterprise is supposed to make contact with and learn about new life forms in a peaceful way. On the other hand, the Borg are insanely dangerous to get anywhere near to, especially if the collective feels threatened, and they killed some Enterprise crew mates. Whatever should Picard do?
In my opinion... try to destroy the Borg. Though quantifying the value of a life at all is sketchy, the rule that the life of each sentient (self-aware) being is equal seems fair to me. By that rule, the Borg collective is one sentient being. Considering that they have the potential to kill all humans, it is justifiable from a moral and evolutionary perspective to kill one sentient life to prevent that from happening.