re: If the Rapture happened, and you were left behind..yes or no to the Mark?

I'm guessing there may be some roots in misinterpretations or evolving notions of "the remnant."

I've also known some mainline protestants who were extremely concerned about being part of "the elect" who are called home to Jupiter.

There are some different and conflicting traditions there that I've really put much time into studying, but I imagine there are some historical reasons for a large audience to embrace LaHaye's lasted fiction-based innovations. There's also been some growth in Catholic apocalyptical fiction in recent years for some reason, but nothing as successful as LaHaye.