A follower of this blog sent me the idea for this blog topic (and some great ideas - thank you!). You may, too, have encountered this.
"I am amazed, to no end, at the ignorance of some believers - when I suggest that I am a skeptic or an atheist and they respond with: 'So you are into Scientology' (often not even stated as a question)"
He suggested that he tries to respond with "You have no idea about Scientology and other religions but you're certain you chose the 'true' one?".
I have often encountered the "Are you a Scientologist?" or "So you believe in Christian Science?" when I mention that I accept the theory of evolution. It is clearly a sign that the person knows little about science and nothing about either Scientology or Christian Science. (I've often remarked that 'Christians' will argue with me against Christian Science - they'll say "It's not Christian" and I'll say "It's not science".)
Scientology, for those that don't know, was created by man (as most religions seem to be - given their misogynistic views) - a man - L. Ron Hubbard. He was a science fiction author (many would argue that Dianetics was his greatest work of fiction) who created Scientology in the middle of the 20th century. It is not based on science, it is not based on reality - it is a money hungry cult (the difference from other religions is so subtle that there isn't one).
Christian Science (Church of Christ, Scientist) was created by a woman (wow!), Mary Baker Eddy (and she didn't do anything to shed the "master" teachings of Christianity and other monotheistic religions) in the late 1800s. Christian Science preaches about healing oneself without medical intervention and, as I recall, about the idea that matter only exists if you believe in it (and that matter really doesn't exist).
For someone to ask if I'm a Scientologist or if I'm a "Christian Scientist" suggests that they are not aware of the teachings and beliefs of either of those religions and one must wonder if they know much about competing religions aside from a headline in the newspaper or what their church leaders have decided to tell them about it. I don't think it'd be a stretch to say that they probably don't.
In reality the problem is deeper than that - many people know little about their own faith and only have heard or accept the whitewashed versions told to them. Many haven't read their bible in its entirety and many are rather ignorant about the history of their faith. In street-level debates, I've seldom encountered a believer who is even aware of completely undisputed facts about Christianity. During a recent conversation with a believer, they expressed utter disbelief when I stated, factually, that the gospels were not written down until decades after Jesus' supposed death and resurrection (I could only imagine their response had I mentioned that Jesus had as many as 18 foreskins!).
I think this only goes to demonstrate that believers don't accept their religion to be true because they've carefully examined a variety of faiths and picked the one they believe is most plausible. It's likely that they hold to their current faith because they were indoctrinated into it and haven't dared question it because of the strict protestations of their supremely jealous non-existent sky-daddy.