Evolution deniers often claim "I used to believe in evolution... until I looked into the science." Many of them are lying, especially about the science part, but what if some of them really did change their minds?
Similarly, one environmentalist (Mark Lynas) changing his mind about transgenic crops isn't evidence, one way or the other, that they are safe or useful. I don't have much to add to what Chris Smaje and John Vandermeer have written about this high-profile "defection."
My own guess is that the risks of current transgenic crops are less than many environmentalists fear, but the benefits (and potential benefits, at least within the next decade or two) are less than GMO supporters promise.
But, you may ask, as long as investing in biotechnology research will provide some net benefit, shouldn't we do it? As usual, an analogy based on rhizobia may be useful.
How should we view a rhizobial strain that provides some nitrogen to its legume host, but occupies a root nodule that would otherwise have been occupied by a more-beneficial strain? Wouldn't we be better off if the less-beneficial strain were less abundant in soil? Similarly, if some of the money invested in biotechnology would otherwise have been invested in more-beneficial ways, such as developing agricultural methods informed by ecology and evolutionary biology, wouldn't we be better off investing less (but not zero) in biotechnology?