Some films show unnatural jerky motion at 24fps because the director intended it to be that way.
Its not that 24fps isn't enough, its because they either shot the scene with a 90 degree (or less) shutter angle, or deliberately dropped frames to give it that 'edge of your seat' feel.
24fps is enough for perfectly smooth motion, its just that some people find films like Saving Private Ryan uncomfortable to watch.
Switching on motion interpolation can relieve the discomfort, but totally changes the mood and feel of the film.
For those that leave Motion interpolation turned on, I'd say don't blame 24fps for lack of smoothness.
For those who want to beat the 'as the director intended' drum, I'd say keep educating people, but appreciate that some may find certain scenes uncomfortable to watch without it.
There, that's me sitting on the fence again!