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I did not explicitly say it, but I hope to god that what people come away with from that excerpt is not anything having to do with the general utility of marches.
The technique under discussion in the example (marching) is completely unimportant to the general lesson, particularly before context is added: a staunch ally brought the maximal amount of pressure to bear on the administration in a troubled time, in order to stand up for what was right and for his own constituency.
Context is crucial in the specifics: 100,000 black people marching on Washington DC in 1963 was controversial enough to the establishment; in 1941 it's even more significant.
Secondly, as the excerpt clarified, people at the time had not only been marching but striking and protesting and even engaging in general strikes.
The techniques used to effect change vary by the context, including the times.