a. I deconverted from Mormonism.
b1. I think the SGU was, more or less, my introduction to the skeptical community. I can't remember how I found it. Irreligiosophy helped a lot. Also, the Mormon Stories podcast.
b2. The main thing that helped me was to see the underlying foundation of Mormonism. I saw a lot of "mellowing" of the LDS church over the years and, to me, it violated a central principal of the religion; that what was being taught today was the same since Adam and Eve. i.e. A&E were Mormons, as were Noah, Moses, Jesus, etc.
The short version is that I saw serious changes that had taken place in the Church with no real reasoning as to why those policies existed in the first place.
b3. The "arguments" I found most effective weren't really arguments. They were simply people saying, "this is what you believe." I was able to look at things like obscure passages from the scriptures and read obscure papers from various church leaders. When I asked other people about them, I was given stupid (non)answers.
To me, it's a simple process of de-conversion. Just point out things that people are supposed to believe and ask them if they really believe those things. If they do, so be it. If not, then why.
My personal favorite tack these days is the 10 commandments. I ask people if they believe them. I ask them to name some of them. I ask them how they think Moses and his people got them.
Most people picture Moses coming down a mountain with tablets of stone written by god. And that's what they are taught to believe.
It comes from here:http://skepticsannotatedbible.com/ex/20.html
But what they don't consider is that *those* were given verbally. The *real* 10 commandments (the ones Charlston Heston had) are found much later:http://skepticsannotatedbible.com/ex/34.html
That set was the second set of tablets carved in stone. The first set, a few chapters earlier, were also carved in stone but Moses broke them when he saw the people worshiping a golden calf.
Anyway, at some point, people will either *get* that they have been lied to, or they won't. I did. It pissed me off. So I stopped practicing. It took almost another year for me to become a full-on raging atheist.