Horseshoe theory isn't broadly accepted. The Wikipedia page for it is full of academics pointing out how terrible it is as a model for understanding the far left and the far right, and this summarizes it well:

The horseshoe theory is not widely supported within academic circles; peer-reviewed research by political scientists on the subject is scarce, and existing studies and comprehensive reviews have often contradicted its central premises, or found only limited support for the theory under certain conditions.

The "stethoscope theory" is even less supported. Where on Earth did you get the idea that any of this made any sense?