My understanding is that many kind of pesticide and herbicide were proven to have adverse health effects, like cancer. But not all of them.
In the lack of information of which specific pesticide/herbicide/... was used on a given piece of "conventional food", and in-depth knowledge of the toxicity of each of them, I consider the "chose organic when possible" to be a reasonable safety measure. Some of the "conventional food" will not be any worse than the organic, some will be worse, and since I can't tell them apart, I consider "non-organic" to be weak evidence towards "slightly toxic".
The other point is, regardless of the effect of the food itself, some of the "conventional farming" does damages to the ecosystem - there is evidence it does pollute underground water, kill bees, ... Not all of it, but once again, I lack the ability to tell apart a "low-impact" conventional product from a "high impact" one, so I tend to chose organic also because of the effects not to me when I eat it, but to the everyone when it's produced.
Both of them are relatively weak reasons, but buying organic when possible only has a weak cost (it's not that much more expensive, and I can afford it).
i find that heuristic to be silly. Pesticides that are used in conventional farming are heavily regulated unlike ones used in organic foods.
I've been wondering whether there's any solid evidence that organic food is healthier than conventionally produced food-- the arguments I've seen on the subject have been theoretical/aesthetic.
I'm interested in anything in the range from personal stories to scientific studies, but would prefer to avoid extremely general arguments or claims that people who prefer one or the other are demonstrating character defects.
Edited to add: Thanks for the replies. I'm hoping for experiments which test the effects of food produced in various ways on organisms, especially multi-cellular organisms. It was interesting to find out that plants which have to fight off insects for themselves have more mutagens.
The mutation experiment is very cute, but it leaves out the possibility of damage that isn't related to mutation-- for example, hormonal effects. Also, if it's done on a standard bacteria acquiring the ability to make a particular nutrient, this might not be a test for mutation in general.
I realize experiments on organic vs. conventional would be difficult, especially if you're tracking human health. It would be very hard to avoid confounding factors like other lifestyle factors and income.
"Conventional food" is actually a large blob of a concept-- different pesticides, fertilizers, etc. are used on different foods at different times, so finding out what people are actually exposed to would be difficult.