Thanks, Aurora — I hope all is well with you too! RebDoniel, Noahidism is not a fallacy. It’s a reality, and a necessity. Many people nowadays become convinced that Orthodox Judaism is true, and other religious are not. Not all of those people can convert, for whatever reason — for example, many do not live near Orthodox communities.
Some of those people do not want to convert, because they understand that they do not to convert to earn a share in the World to Come (or, more kabbalistically speaking, accomplish their tikkun, their soul correction.) There is a huge difference between following the Noahide laws and being a completely observant Jew, because there are many details of Jewish law — Shabbos, Kashrus, davening, taharas mishpachah, etc. — which are not required of Noahides.
Now if a Noahide has a strong desire to join the Jewish people and follow all the mitzvos of the Torah, then that person is probably meant to convert. But not all Noahides have that desire. That said, I’ve head that many people active for many years in the Noahide movement become dissatisfied with “merely” being a Noahide and convert.
The “Aleinu” prayer, which is recited three times a day, looks forward to a time in the future in which all the nations will follow Hashem and cease all idolatry. That doesn’t mean everyone will convert. Most of the world will be Noahides; only a minority will convert. Once the Messianic era begins, converts will no longer be accepted. Presumably, Moshiach will inspire the whole non-Jewish world to become Noahides (perhaps retaining some of their non-Jewish beliefs and practices if they aren’t forbidden to non-Jews).
Noahidism as a “religion” is only a recent phenomenon because, well, freedom of religion and the dispersion of good information about Judaism through books and the Internet, is a really new thing. In the past, people convinced of the truth of Judaism just converted or forged their own individualistic path. Now, there are enough believers unable or uninterested in conversion for Noahidism to become a viable movement. Even so, it’s a pretty small movement and I’ve never met an actual Noahide.