If we were to use Sand´s logic, there would be no such thing as secular Christians, Muslims or Buddhists either. People are free to identify with any religion, community or nation they wish based on self-definition (such as Benedict Anderson writes in "Imagined Communities"). Communities themselves may also define individuals as members or non-members based on their own rules (such as somebody who "feels Jewish" but isn´t recognized as such by the community). Shlomo Sand´s book is simply one more opinion - one that very few people share, and therefore is irrelevant in a world of democratically defined communities.
Merkel says would welcome constructive Iranian role in any Syria talk (Reuters)
from the article: The Gospel according to Sand: We are not Jews