Once at a lecture, when the speech was completed, an attendee stood and said that I strongly object to how you address us as being Jewish. The speaker answered by clarifying that he thought he was speaking to a Jewish crowd. The response was that "I am not Jewish - I am a JEW." something is 'ish' if it has an aspect of that thing in it, like blueish or softish. I am a JEW, without the ish".
Perhaps the greatest blow to Judaism was created by those who present Judaism as a religion. Just like the major religions of the world - the synagogue is the Jewish parallel of the church, Chanukah of Christmas, rabbi of the priest, and the Torah of the Bible. If you follow this thinking you become an adherent of that 'religion' because you choose to believe and practice your life in such a way. However, if you wake up one day and decide that you no longer believe in that 'religion', then you are no longer part of it. As a result you follow it's edicts as long as you believe in it.
Unfortunately for those who would like an easy way out, Judaism is not ‘just’ a religion. We are Jewish because our mothers are Jewish going back to Sara our Matriarch. Being a Jew is like being of a certain lineage, whereby you are from the descendants of Abraham and Sara, or you converted properly to join the family. Once born a Jew, you will be that way the rest of your life, whether you like it or not. We cannot change our race, or who our parents are. These are facts that are part of our essence whether we like it or not.
So if Judaism is not a just religion, what else is it? The Torah answers this question clearly. It is a covenant - a binding commitment from G-d to the children of Abraham and the children of Abraham to G-d. It is being part of a people with a purpose that will last through the eons of time, and creating a relationship both with the world and G-d in a balanced way that joins Heaven and Earth. Whether one adheres to the principles and beliefs is a matter of personal choice, but it does not affect the reality of one's lineage.