They absorb carbon monoxide and carbon dioxide and give out oxygen. What could be more desirable? And they look good in the bargain. Stop chopping down the rain forests and plant more saplings, and we're on our way.
Why is it, I wonder, that anyone who displays superior athletic ability is an object of admiration to his classmates, while one who displays superior mental ability is an object of hatred?
Intelligence is an extremely subtle concept. It's a kind of understanding that flourishes if it's combined with a good memory, but exists anyway even in the absence of good memory. It's the ability to draw consequences from causes, to make correct inferences, to foresee what might be the result, to work out logical problems, to be reasonable, rational, to have the ability to understand the solution from perhaps insufficient information. You know when a person is intelligent, but you can be easily fooled if you are not yourself intelligent.