You don't have to aim to topple the industry, just pressure them to make changes, with the implied threat of a boycott.

I'll admit that approach works better with a simpler less wide ranging issue. Examples off the top of my head, in the UK I don't believe you can buy non fair trade bananas from any of the major supermarkets, and most eggs now seem to be free range.

Yes, most eggs. I just checked and 44% are intensively farmed(not free range). Generally most use in processed food and catering will be of a lesser quality standard. Funnily enough the environmental impact is usually less for intensively farmed food.

"Funnily enough the environmental impact is usually less for intensively farmed food"

What are you comparing here? Could a mega farm invest in slightly more efficient processes than a mere 'very large farm'? Possibly. But by that time you've already got all the issues of grubbing up hedgerows, mono cropping, reliance on artificial fertilizers, soil erosion, etc.

A small organic subsistence farmer isn't going to have anywhere near the same impact. Now you may not be able to feed the world using that model, but I don't think its fair to say that the environmental impact is worse compared to intensive agriculture.