Answer:
Rand's assertion that the validation of value judgments can be achieved by reference to the facts of reality, thereby bridging the gap between "is" and "ought," is a central tenet of her Objectivist philosophy. However, the critique you presented suggests a potential flaw in her argument – the idea that existence determines ethical essence might imply that living entities come pre-equipped with their ethics rather than deducing them from a factual sub-stratum.
This could be seen as a challenge to Rand's ethical project, as it questions the foundational idea that one can derive ethical principles directly from the observation of reality. While Rand's approach attempts to ground ethics in the objective nature of existence, the criticism highlights a potential tension between the claim that "existence is ethical essence" and the idea of deducing ethical principles from observable facts.
Whether this is fatal to her ethical project depends on one's philosophical perspective. Some may argue that no moral philosophy completely bridges the gap between "is" and "ought," and Rand's attempt is as valid as any other. Others might see the critique as a significant challenge that raises questions about the coherence of Objectivism as a moral framework. Ultimately, the evaluation of this potential flaw in Rand's argument depends on the depth of one's commitment to her philosophical framework and the weight assigned to the issues raised by critics.