Your comparison of depopulation to "overpopulation in an already overpopulated world" is hardly just. Really you are comparing population decline with population growth, but with the latter in a very particular context in which it is known to be harmful. In contrast, nobody is concerned about population growth among polar bears (but many seem concerned about their potential depopulation).
Regardless, the concern of the article isn't even whether or not depopulation is bad; in fact it states: "In the modern era, population decline itself need not be a cause for acute economic alarm." Rather the concern is that Russia's depopulation is fueled by increases in illness and mortality. Just my personal opinion, but death and disease are bad things. The article claims that, furthermore, they are bad things for economic growth over the long term.
GM is a modern farming practice that is horrendously underused, and GM can wipe out most of the disadvantages of intensive farming - GM crops can fix their own nitrogen and repel pests without pesticide. They can also be designed to grow well in 3rd world climates and contain extra nutrients.
Yes, we need more "techniques" such as those that lead to an infection of spinach with some bacteria that is later traced to a gut of a wild boar used as a fertilizer.
I don't think you are remembering that case correctly. The animals are not being used as fertilizer. Instead, they are breaking through fences and contaminating the fields through defecation: http://www.capitalpress.info/main.asp?SectionID=94&SubSe...