The problem is actually more subtle than our punctuation system can deal with except by resorting to reasoning beginning with "It seems..."
Our punctuation system proposes to convey both intonation and separation of words into blocks of meaning. To expect several symbols to do this well is to expect far too much in some situations.
(Incidentally, this is the source of an underlying principle in the classical manner of interpreting statute law: the punctuation and capitalization of an act are of no consequence and the meaning of the act must be extracted from the words alone. An interpretation that does no violence to a possible meaning of the words without their dress of punctuation and capitalization is considered a possible valid option.)
Perhaps this is the problem: written English is not capable of expressing many subtleties of the spoken tongue.
In written Spanish, rhetorical questions can begin with an inverted question mark and end with either a full stop or exclamation point: ¿Am I a fool!
In written English we have no such clever devices. This would seem to indicate that we must force ourselves to recast perfectly acceptable oral sentences into reasonable equivalents in the written language.
A good writer, instead of transcribing his speech into writing should rather try to express his underlying thoughts well in the written vernacular and dispose of, as far as possible, the subtleties of the spoken phrase.
Crassly put, maybe Rachel Carson should have recast her sentence. (And, oh so certainly!, I should have avoided italics by writing better.)