Consider: The effectiveness of brakes depends on the size of the patch(es) of rubber (the tire contact patch) on the braking wheel(s), and on the downward force applied to those patches; a bigger patch is better. The rear tire is less effective than the front due to weight transfer during braking. Skidding is much less effective at stopping than not skidding.

The rear coaster brake combines the worst of each of these elements.

• It uses only one tire rather than two, minimizing the contact patch.
• It works only through the rear tire - much the less effective of the two.
• Maintaining maximum braking without skidding requires a deft touch - something best done with the hands rather than the legs you're standing on. That's why coaster brakes are renowned for skidding.

Okay you like coaster brakes. Just don't fool yourself into thinking that they anywhere near as effective as other systems at stopping a bike.