Why do you think userbinator was perplexed?
Instead of the slavery example, consider how a white man in the 1950s could be perplexed that another white man would want to share civil rights equally with women and blacks. After all, both white men were brought up in a system which benefited them over others - why change?
Or how a native born citizen could want to allow more immigration, when another native born citizen could be perplexed about how that can reduce the opportunities for native born citizens (eg, "they will take our jobs").
No idea. I am still perplexed why you don't seem to understand that your argument is totally invalid, since the comparison does not make sense.
My argument concerns the reasoning behind the perplexity. Since you don't understand the perplexity in the first place, you must not understand the reasoning either, which means your comments have no bearing on the topic, why is why you think I'm not making sense.