We often say that all religions are equally absurd and that the only reason some seem more absurd is that we are less familiar with them. Islam will seem strange to someone living in a thoroughly Christian culture, and Christianity will seem odd to someone raised in a thoroughly Islamic culture. But one of the things most religions have going for them is the difficulty in disproving them. That is, most of the popular religions have survived in part because they do not base themselves on concepts that are extremely easy to disprove. However, there is an important exception in the case of the Mormon religion.
We can certainly attack the concept of an omniscient, omnipotent, and loving god, highlighting its logically incoherent nature. But this is very different from something like conclusive proof that Jesus or Mohammed never existed. Even if there are compelling reasons to suspect that Jesus never lived, this is a far cry from proving that he did not. As absurd as Christianity and Islam are, it isn't like most Christians and Muslims cling to beliefs that have been thoroughly debunked (or am I being too generous here?).
This is not the case with Mormons. The Mormon accounts of Joseph Smith, with his golden plates and seer stone, are more than implausible. By rooting their religion in the modern era, the Mormons have made it far easier to evaluate and even disprove many of their central claims. As an example, we know that Joseph Smith was a real person; in fact, he was a con man. We know that the material claimed to have translated, his book of Abraham, was fake. Moreover, genetic testing has revealed that Native Americans are not Israelites as Mormons believe.
From an atheist perspective, it would be easy to claim that adherents of all religions are equally deserving of mockery for what they believe. After all, each of the major world religions demands irrational and often destructive beliefs from adherents. Still, Mormonism is one of the only examples of a religion I have found that is based on a set of claims that are not only demonstrably false but that have been shown to be false. This seems to put Mormons in a somewhat different category as adherents of most other religions.