Since you obviously didn't play the first game (since you don't know why you should be opposed to Cerberus), you might not understand that Cerberus is basically the well-funded Al Qaeda of space. Giving them the technology doesn't necessarily mean they'll make a reaper, but it means that they'll have an advantage over every other race in the galaxy which they will inevitably use against them.
Furthermore, you should realize that paragon and renegade in this game are not good or evil. Rather, what they boil down to is unity and compassion vs. human imperialism and tough love. In this way, moral choices aren't the same, stale BS we've been playing in Bioware games since KotOR.
tl;dr paragon and renegade aren't plain good and evil and you need to play the first game to understand why Cerberus shouldn't be trusted with the tech.
Furthermore, you should realize that paragon and renegade in this game are not good or evil. Rather, what they boil down to is unity and compassion vs. human imperialism and tough love. In this way, moral choices aren't the same, stale BS we've been playing in Bioware games since KotOR.
tl;dr paragon and renegade aren't plain good and evil and you need to play the first game to understand why Cerberus shouldn't be trusted with the tech.