I wouldn't say they are a stumbling block to the unsaved because you're assuming people should be saved based on logic. The vast majority of Christians in the scriptures (all?) were not saved based on logical reasoning pertinent to modern western society.

It's a bad premise, that to think a person should be a Christian because they went through a series of higher intellectual reasonings. If this were how God did things, then a vast majority of the human population could never be saved due to their lack of intelligence or knowledge.

God is intentionally foolishness to the wise: "but we preach Christ crucified: a stumbling block to Jews and foolishness to Gentiles," - 1 Cor 1:23