Anyone citing seriously the Seralini et al. study immediately loses all credibility in my eyes.
That article was retracted chiefly because many professional statisticians (I am one) pointed out that this study was, from the point of view of basic statistical methodology, a complete joke. In no significant way did this study establish any correlation between GMO and rat tumors (which is not to say it can't exist. Just that the data collected from this particular study does not prove anything).
It is laughable how the piece you link to suggests a big conspiration because the paper was retracted despite its original publication undergoing a "rigorous peer review". The fact of the matter is, peer review can fail big time (given the number of submitted scientific papers, that is hardly a surprise), and journals should definitely retract papers when it turns out after publication that they are a methodological disgrace.
Expose questionable scientific behavior practices, undisclosed conflicts of interests, biased studies, question established truths -- I am all in favor of it. But using bogus (and in this case sensationalist) studies to do so is self-contradictory. Bad science should be countered by good science, not by wishful thinking and vague conspiration theories.