Idea/ideal are homophones/heterographs in certain Southern accents. Pronouncing idea as "ideal" doesn't necessarily indicate that the speaker doesn't know or distinguish between the separate meanings of the words, though that may be the case in some situations. Another example that may provide some understanding for those who are quick to label these individuals as stupid is the pronunciation of pin and pen in the American South. Though the shared pronunciation leans toward the more standard pronunciation of pin, the speaker obviously isn't requesting a "pin" when he or she is asking for something to write with.