They disagree on a lot of things, but they also disagree on a lot of things with moderate people, so that observation alone doesn't refute "far-left and far-right are closer to each other than they are to the center".
Of course the horseshoe effect is not some objective truth that's true in every country, that would be silly. I think the interesting part of it is that extreme ends of any political spectrum experience a similar environment: they are often shunned, distrust the mainstream media, attract social outcasts, etc. Just the shared experience of being on the edge of the spectrum often leads to similarities between them.
Of course the horseshoe effect is not some objective truth that's true in every country, that would be silly. I think the interesting part of it is that extreme ends of any political spectrum experience a similar environment: they are often shunned, distrust the mainstream media, attract social outcasts, etc. Just the shared experience of being on the edge of the spectrum often leads to similarities between them.