When monarch caterpillars ate those leaves, they died. That happened in a lab, not in nature. No one knows yet whether it happens in nature or happens to other kinds of butterflies or happens to other innocent creatures that run into pesticide-producing corn. The point is not that biotech kills butterflies, though it might. The point, made by ecologists for years now, is that gene-spliced inventions are being spread over millions of acres at a hectic pace without any idea what their effects might be.
Unwelcome surprises are almost inevitable.
So our government and several European governments have declared. Whether you believe them depends on how much you're inclined to trust your government. Don't trust that tractor. Europeans, having recently heard from their governments that mad cow disease is no health threat whatsoever, are not in a trustful mood. They insist that GM foods at least be labeled so consumers have the option of avoiding them.