So, by order:
1) What's wrong with conventional farming?
More than anyone could properly learn about. Other than getting a Global Resource Systems or Agriculture degree, many books including Fast Food Nation by Eric Schlosser or The Food Revolution by John Robbins, as well as countless books written by vegans/vegetarians/scientists/farmers/environmentalists can let you know about the food issues facing our food security or the ethics of farming animals (oh, a good one for that is Peter Singer or Tom Regan). You'll note that I'm not vegan or vegetarian, but I definately think the conventional method of farming's largest short term implications is how we treat the animals there.
2) Are pesticides really that harmful?
I believe Silent Spring by Rachel Carson is the one to read for the answer to that one.
3) If so, why hasn't this issue received the same attention as, say, sweatshops or conflict diamonds?
Given that there is the Organic movement that has a full fledged and legal method of deliniating its products from conventionally farmed goods, as well as the fact that there are entire degrees based around this issue, as well as the largest media splash about this issue (Silent Spring) 20 years ago, and that vegetarianism and veganism are very VERY large movements, I'd say that the conventional farming has received much more than either of those other issues. They are just more modern and en vogue.
4) Also if so, why are they legal? If it's because of big agribusiness, why do they have so much influence?
I believe you just answered your question with the word big. Given that, in North America, our political systems are based primarily around the idea of interest and lobby groups bringing the issues to the government (more so in the USA than Canada, but we often follow suit culturally, which means we end up doing similar things and thinking similar things are acceptable), these agribusinesses get more say. Which is also, by the by, why the copyright legislation changes everytime Mickey Mouse enteres the public domain.
5) What's better about organic standards?
http://www.certifiedorganic.bc.ca/
Remember that organic standards do differ slightly across regions, so it's good to become knowledgeable about more than just BC. Or, just only buy local (which is also good). Or, learn about the body that each of those regional authorities get their authority from:
http://www.qai-inc.com/
6) Isn't the natural vs. synthetic distinction pretty arbitrary and not very scientific?
Certified organic is not about natural vs. synthetic. It is about certified organic versus not. If you become aware of the rules that certified organic entails, and what most conventional farming entails, you understand the distinction better.
7) Can't genetically modified organisms be beneficial, like vitamin-A-rich golden rice in Africa for example?
Yes, but I believe that accounts for less than 1% of the geneticall engineered food grown (created?) in the world. Monsanto accoutns for over 99% (not an exaggeration) of the genetically engineered food industry in the world, and mostly sells things like "Round-Up Ready" crops, whose sole purpose is to resist stronger pesticides (read: Round-Up) that Monsanto sells. That, and it heavily attributes to the problem of monoculture even when used in a non-environmentally devastating way, which has its own issues.
I know you didn't address it directly, but I feel that the issue of "genetic food is more productive" needs to be addressed before moving on. Given that there is a vast global surplus of food (something like 50% of food is thrown out before it even reaches a kitchen in North America, or that India, in an attempt to keep world grain prices down, throws out enough grain every year to feed Afica's entire population, or any number of staggering facts) I simply do not believe the slight gains in productivity outweighs the incredibly large environmental problems that the use of genetically modified foods either produces directly or indirectly.
8) Organic food is more expensive and therefore a luxury that is unavailable to some. What if you can't afford it?
I do not believe such a person exists. What I perceive most people doing is shifting away from the ethical choice of organic (or better) food, towards other luxury items (such as movies, video games, new clothes, more meat than you actually need in your diet, drugs, cars, shall I go on?). Given that I have met single mothers on welfare who buy only organic food, this argument doesn't hold in the western world.
Also, after viewing the film Deconstructing Supper I am almost certain that there is almost no one in the world that can't afford organic food (maybe not certified, but that's another issue). Given that in some of the poorest places in the world, such as some provinces in India, there are strong anti-pesticide and anti-genetic modification, and other things of the so-called "conventional" farming method, I don't really think this is ever a valid excuse.
9) You have found satisfactory answers to many of these questions after years of hard study, research, and deep thought. But as an average Joe, I don't have time to do the same research; besides which, it's probably very hard to find an unbiased, reliable opinion! I would like to have a positive impact, but I would like to base my decision about how to do that on a solid, scientific foundation, rather than on hearsay and trusting the opinions of people like you who are seemingly more knowledgeable (or at least who hold stronger convictions).
That's why we agree, as a society of lazy affluent and wealthy individuals interested in specialisation, not breadth of knowledge, agree on listening to so-called experts. Like me. Or, if you don't trust me, then you trust large organisations involved in these issues or people with firmly based academic studies on the matter. Yes, I am willing to acknowledge that there are scientists who support conventional farming. There are also academics who support sweatshops, yet I don't agree with them either. A large, existing body of knowledge exists that is firmly on the side against conventional farming (the largest supporters of conventionally farmed goods are the small wealthy companies who make it, as well as the average uninformed consumer, as well as some other outliers).
If that isn't good enough, well, that means you actually have to learn about the issues.
