Sometimes one reads a poem and believes that the poem expresses contradictory ideas, even if it is a great poem.
Evidence
No one who is writing a great GP → ~ICI poem intends it to communicate contradictory ideas.
Sometimes one reads a poem GP + BCI and believes that the poem expresses contradictory ideas, even if it is a great poem.
Conclusion
So it is wrong to think that the meaning of a poem is whatever he author intends to communicate to the reader by means of the poem.
Evaluate
The argument assumes that if BCI → CI the reader believes that a poem expresses contradictory ideas then contradictory ideas are part of the meaning of a poem.