As for fisting, I don't find it scary at all. If anything, I find it surreal, otherworldly, and spiritual. Almost like doing some seriously heavy drugs without the drugs involved. It's incredibly intimate and requires an intense amount of trust and subconscious connection with your partner. Not a light breezy activity to be offered casually, IMO.
I never try to fist anyone who isn't explicitly asking me for it unless his asshole is so hungry for something bigger than my largest toys that my fist is the only thing left to suggest! But these guys are typically VERY experienced with anal play and have a huge amount of comfort and control with their own anal muscles.
I always say fisting is like trying to bench press 300 lbs... you don't walk into the gym on Day 1 and try it, not do you expect that within the month you'll be expected to reach that level. All muscles (including anal muscles) must be trained slowly and carefully and gradually over time, so that they can strengthen in a healthy and safe manner.
And as with my metaphor, neither bench-pressing 300 lbs nor getting fisted is everyone's goal in life. For some people, some simple muscle toning or occasional PM to stay healthy is all that is desired. And there's absolutely nothing wrong with that. Having personal limitations is perfectly normal.
For the extremists who have a lot of experience with anal play and crave the extra intensity of swallowing one of my limbs with your ass... well.. what can I say... except- CALL ME!