What causes spiritual blindness?
In "Biblical Perspective" I.C. Holland writes concerning 1 Peter 2:8…
It is no wonder that sightless people stumble. Spiritual blindness is worse than physical. Witness the cases of Fanny Crosby and Helen Keller. The cause of stumbling in verse 8 is identified as being disobedient. Disobedience and unbelief are inseparable Siamese twins. Although there are professed members of the Church who are insincere and substandard, the cause of stumbling is not the fault of the church. It is identified in 2 Corinthians 4:4: “The god of this world hath blinded the minds of them which believe not.” The word appointed does not mean that they were foreordained to be lost, but that infinite justice forestated that “the soul that sinneth” shall die. Sinning is volitional. It is a choice.
Source: Building Christian Relationships: Adult Teacher's Insights, page 18.