In the ethical debate on genetic modification (GM), it is common to encounter the claim that some anti-GM argument would also apply an established, ethically accepted technology, and that the anti-GM argument is therefore unsuccessful. The paper discusses whether this argumentative strategy, the Similarity Argument, is sound. It presents a logically valid, generic form of the Similarity Argument and then shows that it is subject to three types of objection: (i) It does not respect the difference between pro tanto reasons and all-things-considered judgments; (ii) it relies on the unproblematic transferability of reasons from one case to another; and (iii) it runs the risk of equivocations, especially in cases where the anti-genetic-modification argument relies on gradable features. The paper then shows how these issues play out in three specific Similarity Arguments that can be found in the literature. Finally, the paper discusses what conclusions we can draw from the fact that genetic modification and established technologies are similar for the ethical status of genetic modification.