Metagenomics is a burgeoning field enabled by cheap sequencing firepower -- which grows cheaper each year. You take some interesting microbial ecosystem (such as your mouth, a septic tank, the Sargasso sea), perform some minimal prep, and sequence everything in the soup. The results find everything in the sample, not just what you can culture in a dish.
Now in Nature we can see the backlash -- angry microbiologists irked at uneducated oafs stomping their turf. One complaint (scroll to the bottom) is the oft used term "unculturable species" -- i.e. the new stuff that metagenomics discovers. Quite appropriately, the microbiologists cry foul on this aspersion against their abilities, as the beasties aren't unculturable, just haven't been cultured yet.
The new letter says 'Amen' and goes on to gripe that sequencing unknown microbes is no way to properly discover biological diversity, only culturing them will do.
IMHO, a lot of this is the usual result of new disciplines with eager, arrogant new members (moi?) wading into the domain of old disciplines. According to my microbiology teaching assistant, a molecular biologists is defined as "someone who doesn't understand the biological organism they are working with". Similar issues of "hey, who's muscling in on my turf?" beset chemistry, as illustrated in this item from Derek Lowe's excellent medicinal chemistry blog.
These sorts of spats have some value but aren't terribly fun to watch. Worse, the smoke & dust from them can obscure the real common ground. There is already at least one example of using genome sequence data to guide culture medium design. Perhaps future metagenomic microbiologists will make this standard practice.