The "Islam is the fastest growing religion and therefore it is true" argument

The argument: Because Islam is the fastest growing religion, Islam is true.

The response: Simply because a religion is growing the most quickly does not mean the religion is necessarily true. If this were true, we would have to conclude that Christianity was true because at one time it was the fastest growing religion, I agree that Christianity is true, however to argue in this manner is invalid. Communism, grew quickly as well, it must be true then in this logic, apparently. If this logic is correct we must conclude that (I) Christianity was at one time true and that Communism was true as it was one of the fastest growing types of government.

The logic is:
I) Because Islam is the fastest growing religion...
II) Islam is true.

Therefore by that logic:
I) Because Christianity was the fastest growing religion...
II) Christianity was true. (As it spread very quickly)

Also by a similar logic:
I) Because Communism grew very quickly.
II) Therefore Communism is true.

See below for other articles

Islam, the Incredible Shrinking Religion by  Anthony Rogers