I really don't know the intention of the writer of this article....perhaps it is simply an intention to be an unbiased religion reporter.
I will say that any arguments, opinions, etc. which use comparisons as a basis for some proposed view (i.e. Scientology isn't much different than Catholicism) is specious reasoning.
Scientology is indeed a corrupt organization that simply gloms as much money as it can from its adherents. The writer seems to poo-poo the idea of Xenu as unimportant or even not essential to the scientology organization when in fact it is THE central tenet of the scientology belief system.
This is a very light-weight article and I can't imagine the reasoning behind it nor can I understand why Slate magazine would give such a light-weight piece of writing actual space in its pages.