One of several reasons that makes this a bad comparison is that nobody expects to be able to tell by looking whether someone is Jewish. Religious beliefs are an intangible, internal quality, and Jews, like Muslims, Christians, atheists, etc come in all colors and appearances and both sexes. There may or may not be clues, and everyone takes for granted that you don't know people's religion unless they tell you. This is not at all like which sex someone is, which is obvious at a glance 99.9% of the time, and generally takes a lot of effort and money to hide - which means if someone is not the sex they appear, this is an active deception. Active deception is not equivalent to something you would never expect to know without asking.