I suspect if you asked a historian you would get a much more nuanced view of the concept of a movement being "discredited"; especially any American leftist movement that was under significant state suppression for virtually all of its lifespan.
There were possibly more anarchists predating the first Red Scare using violent tactics than state socialists, but Eugene Debs still ended up in prison, and I think it's pretty impossible to claim he was somehow violent.
Further, a historian would tell you that a societies' definition of "violent" is highly contextual; for example, the Occupy movement was classified as "violent" and subsequently subject to significant (and actually, physically violent) repression because as other comments in this very thread have pointed out, they used nonviolent civil disobedience tactics similar to the 60's civil rights movement.
Further, since we can't experiment, we can't make statements about whether or not there were delays in civil rights because of any particular thing. It could very well be that violent tactics from "extreme" leaders like Malcolm X caused backlash, but it might also be that media presentation of these events in a certain way was more causal of backlash, or that these events were polarizing, resulting in some people identifying more with the civil rights struggle while others identified more strongly with white supremacy. So no, it is not enough for me. Why is it enough for you?
The study in question implicitly controls for a number of the factors you raise in the items it compares and convincingly demonstrates a link between contextually-defined violent action and voter outcomes. This assumes you think voter outcomes matter at all - I do, you may not.
If the events in question are polarizing and produce the outcome observed, that would be consistent with both the data and the hypothesis.
What more would you like to see? What would be enough for you? Can there be enough for you, or do you think this question is forever unknowable and to be relegated to the realm of radical hypothesizing forever?
There were possibly more anarchists predating the first Red Scare using violent tactics than state socialists, but Eugene Debs still ended up in prison, and I think it's pretty impossible to claim he was somehow violent.
Further, a historian would tell you that a societies' definition of "violent" is highly contextual; for example, the Occupy movement was classified as "violent" and subsequently subject to significant (and actually, physically violent) repression because as other comments in this very thread have pointed out, they used nonviolent civil disobedience tactics similar to the 60's civil rights movement.
Further, since we can't experiment, we can't make statements about whether or not there were delays in civil rights because of any particular thing. It could very well be that violent tactics from "extreme" leaders like Malcolm X caused backlash, but it might also be that media presentation of these events in a certain way was more causal of backlash, or that these events were polarizing, resulting in some people identifying more with the civil rights struggle while others identified more strongly with white supremacy. So no, it is not enough for me. Why is it enough for you?