That video in the article that splices a Tom Cruise interview with the South Park episode of scientology does a nice job of pointing out just how crazy the religion is and as such, just how nuts Cruise has to be in order to be it's poster boy.

That said, is scientology any more far fetched than other religions? Take christianity and their creation story that involves talking serpents and all womenkind being forged out of the rib of one man. Noah and his ark that housed all of the worlds living creatures. Burning bushes that talk with the voice of god. A savior that comes only to be brutally killed, because... you know, he had to die so that we can live. -Odd stuff.

I'm not sure that alien souls inhabiting our ancestors bodies is any less weird than that stuff. As for whether or not people should attempt to erase their memories, this is a fundamental desire for all humans. This is why we like to have a few glasses of wine, or to go on vacation. These things help us to forget some of our stresses. It's natural. But to want to completely erase your memories is 1. unhealthy and 2. impossible outside of serious bodily harm.

One of my favorite song lyrics is from Wilco's Ashes of American Flags

  All my lies are always wishes
  I know I would die if I could come back new

We all desire to "come back new." This is why the evangelical movement in the US and increasingly the world, is so prevalent. People want a fresh start and religions, Scientology included, like to capitalize on this.

"No thanks," is my response to all of them.