I agree that the horseshoe theory has some merit, but only some. Ideologically and philosophically, the two extremes couldn't be more divergent. However, what they ultimately end up doing will start to bear similarities, the further they are apart, despite their reasons for doing so being completely different.
I actually see strong potential for segregationist tendencies to arise from the far left due to their extremism. Not much different than the far right.
Which is more or less the point of the horseshoe theory, it's about similarities in methods and not ideas. At least how I learned it.