Organic gardening has become very popular in the last 20 or 30 years. One of the very early organisations promoting organics was the Henry Doubleday Research Association (HDRA), now called the Ryton Organic Garden over 50 years ago. After the popularity and subsequent downfall of DDT, no one can deny that herbicides, pesticides and fertilisers, all being chemical in nature, could potentially prove to be a threat. This threat includes destruction of the soil properties, damage to crops, wild life and environment, by excessive use. The problem extends from the macro level, spreading out of control by atmospheric effects and wild life, down to the influence on soil bacteria. The environment, like the human body, should be thought about on a holistic scale.
None of this however, in my opinion, should mitigate against the careful, thoroughly tested and controlled application of scientific knowledge to the enhancement of crop production. Genetic modification also falls into this debate, although, of course, a different concern from that of organic gardening. The Soil Association has much to say on the topic, and there are a growing number of gardeners who try to emulate the standards established by that organisation.
A typical question might be: what is the difference between adding a trace element like magnesium to tomato planting compared with using a rock mineral to do the same job? I suppose the obvious difference is one of time scale; however, it is clear that adding the ground - up rock also changes the soil friability and porosity, but it is not now the same soil you started with.
The debate about organic extends now to the use of nematodes and micro wasps for control of predatory insects and pests. These are gaining in popularity as 'natural' control (even if they were never present in the soil in the first place). As far as I can see, you are still introducing life which may well not have been there originally, and we all know the problems associated with introduction or even re-introduction of wildlife. In the Chilterns the red kite was re-introduced to the area after a long absence. They have multiplied hugely, and I am sure there will be problems ahead.
The main problem with the use of these natural controls is that they have to be replaced regularly, are best used in an enclosed environment, and of course if they are very successful they inevitably die out because their food source has disappeared! The comparison between all methods, based on the carbon footprint, is yet anpother aspect.
Another argument in favour of organic produce is that a) it contains improved nutritional content and b) it tastes better. This tends to be very subjective and is unproven. Many tests have been done in the popular media, and have proved very indecisive. That is not to say that, for example, free range eggs are both more ethical and taste better: it is a different argument. However, after the the terrible problem with BSE and CJD, unacceptable practices had developed with animal feeding, and must not be allowed to happen again.