Hi S., I buy organic for 2 reasons: it's healthier for me and my family, and it can be healthier for the environment.
Some foods, like apples and strawberries and peppers, have such thin skins that pesticides seep right into them--thus you are just eating straight pesticides.
Other foods, like broccoli or bananas, have such thick skins, that the pesticides can't penetrate.
This link lists food by pesticide concentration and is really helpful: http://www.foodnews.org/fulldataset.php
However, there are other things to think about. I know that one of the local apple growers is not rated organic, but they really do work at being sustainable (using the least amount of pesticides), and I tend to buy their apples to support local farmers.
And as far as bananas go, the pesticides used on banana plantations render the workers sterile. They've tried to sue in this country and haven't been all that successful. My huub had cancer and we had to do IVF and it cost us a fortune, but we have our son. I know that the thousands of workers who've been sterilised on banana plantations can't afford to do that. So, I can't in good conscience buy non-organic bananas knowing the human cost contained in them.
Check out http://www.panna.org/ for more on what pesticides really do. Understanding how they work really cahnged my mind about organic, and unless I am supporting a small local farmer, i go with organic.
Lastly, my dad was raised on a farm long before the EPA was around, and he and half of the kids in his highschool have all come down with some type of lymphomatic cancer in their 70's and they all think it was the pesticides.
Thanks for listening. R.