Why is Conversion different?
This is why.
Once upon a time there was an old man who lived in Jerusalem whose name you might have heard. His name was Jacob Katz. He is commonly acknowledged to have been the greatest historian of Orthodoxy, and the Doktorvater of every major Jewish historian in the last generation.
Katz asserted on more than one occasion that schism never comes to the Jewish People based on questions of ritual, belief or political opinion.
It ONLY happens when a group ceases to abide by the basic definition of Jewish Identity: Matrilineal Descent or Halakhic Conversion.
That’s why, as Lawrence Schiffman showed, there was no schism in the time of the Second Temple, Bayit Sheni, despite the many sects involved, while there was a permanent schism with the Karaites (outside of Egypt), Sabbatians, Frankists and now a vast number of American Jews who believe in patrilineal descent and non-halakhic conversion.
Israel cannot afford such a schism, as it is the tribal unity of the country which holds us together.
Reform and Conservative spokesmen address the issue as one of pluralism and personal choice. That, of course, is not the whole story.
Conversion is not simply a matter of self-expression, but one that impacts the entire Jewish People and the progeny of that people. It cuts the ability of Jews to go back and forth in their observance and connection.
NO ONE denies that Reform and Conservative Jews are Jews (if they are born to a halakhically Jewish mother or have had a halakhic conversion) and can worship as they wish (and I am 100% in favor of letting them pray as they wish at the Ezrat Yisrael at the Kotel).
Multiple, non-halakhic conversion casts a deep,irrevocable gap between Jews.
Now, for the present situation I blame the Haredim, the Rabbinate, the government, the Knesset, and certainly the Supreme Court for considering the case at all.
Although that is not the reason for the Supreme Court decision, it is clear that there are perfectly halakhically legitimate ways to make halakhic conversion more accessible without the extremes that reign in the Rabbinic Court System at present. That is the direction we must go, and stare down opposition from both extremes. Otherwise, we are looking at the fraying and undermining of the fabric of Jewish Society in the Land of Israel.