Crunches were so treacherous in the '90s that millions of the lazy and gullible bought ab rollers. They were like training wheels for your torso. They helped make exercise easier, but unfortunately the word "easier" turns a workout into pointless wiggling. Progress still marched on, so soon ab rollers weren't easy enough. Rival products began using it as an example of how impossible situps can be. For example, this man from John "Fitness Personality" Basedow's Fitness Made Simple commercial demonstrates how hard it is for a stupid fucking asshole to keep his head on a speeding Ab Roller:
Is falling off a neck pillow really the main roadblock to rippling abs? Are regular situps actually difficult and dangerous? If you think so, you also think it's normal to run out of breath darting your head toward hot dog smell. You think "lower abs" are the muscles that ghost hunters heave out of the way to search for your penis.
I'm not a physical therapist, but there are millions and millions of 80-year-olds out there today with functional spines and necks. With the blinding speed of aerobics technology, those people grew up at least 450 generations of situps and toe touches behind us, and they're fine. In the '40s and '50s, women did crunches by tying their menstrual belts to a mule and asking their slaves to frighten it. Men only lifted with their legs as a way to signal other homosexuals. The point is, exercise isn't a complicated thing. Anyone telling you differently is trying to justify their physical education degree.