The first sentence sums up the point of my previous comment. I also agree that slavery is bad and that killing people who commit blasphemy is wrong, but I'll explain how these issues should be approached today.
"my conscience does not bear witness to what the Bible says." Maybe not, however, you still do have a moral code, as all humans do. All humans do have a conscious that has an innate sense of right and wrong, even if it is twisted by the world.
Slavery was a social issue of the time, just as homosexuality is today. However, I do not agree with the idea of modern-day slavery or even racism. In addition to this, it was actually Christians who began and ran the underground railroad movement.
In addition to this, the sin of blaspheming is a sin that has been clearly stated to be forgiven by Christ himself “Truly, I say to you, all sins will be forgiven the children of man, and whatever blasphemies they utter, but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin" (Mark 3:28-29). In addition to this, the blaspheming of the Holy Spirit is defined to be continual unbelief in Christ and refusal to repent.
In addition to this, we have been released from the Law of Moses through Christ, "But now we are released from the law, having died to that which held us captive, so that we serve in the new way of the Spirit and not in the old way of the written code" (Romans 7:6). Yet the Law of Moses does give us an idea for what is sin and what is not, "What then shall we say? That the law is sin? By no means! Yet if it had not been for the law, I would not have known sin. For I would not have known what it is to covet if the law had not said, 'You shall not covet'" (Romans 7:7).
Yet the point of Christ's return is that he sacrificed himself for the forgiveness of our sins. "but God shows his love for us in that while we were still sinners, Christ died for us. Since, therefore, we have now been justified by his blood, much more shall we be saved by him from the wrath of God" (Romans 5:8-9). And he came for all "because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved" (Romans 10:9).