I can't say why, but, back on my mission in my first encounters with these kinds of Evangelicals, I immediately felt like their main interest was that they would be happier to see me be atheist than Mormon. It was a few years ago that I ran across an essay by Mormonism Research Ministry (MRM) that said essentially the same thing. They were concerned that Christians were putting too much effort into deconverting Mormons without given them good reasons to convert into Biblical Christianity. Based on that one essay, I think the reason is something unintentional. I expect that most Christians assume that, if they can convince someone to deconvert from the LDS church, it will be automatic for that person to drift into broader Christianity. Statistically speaking, I don't think the assumption is born out. Many LDS when the deconvert, prefer to join the "nones" or move into agnosticism/atheism.
"Never" is a pretty strong word. I doubt I could say "never." However, so much of the root of my "faith crisis" is rooted in prophetic fallibility and scriptural errancy that I doubt I could join any that insist on believing some kind of Biblical inerrancy. I can see branches of Christianity that have a better handle on Biblical errancy than others, and those would be the ones I would be attracted to.
I would say secular critics.
I might need an example of what you have in mind here. Personally, I think my response will depend on the specific issue. Some issues, I would probably agree with the critic, while I would disagree on other issues. A lot of my response would probably depend on whether my counterpart seems interested in exploring truth and right and goodness, or they might seem solely interested in contradicted whatever I might believe.
I would say no effect.
Unknown.