No. It means intestinal fortitude.Like I really care about what your definition of "having marbles" is. This is nothing more than a red herring.
Anyone who reads this can see for themselves what MLK believed. The writings are online at Stanford.
I simply do not like it when people invent beliefs for those whovate not here. We KNOW what MLK believed because we have his writings telling us what he believed.
You are just like those White folks who deny the rebel flag is a symbol of racism even when shown White supremacist groups using the rebel flag as a symbol of racism. Here MLK tells you what he believed in his own words by his own writings and you refute the man.
There is no more disrespect than denying a man his beliefs. That is what you are doing. MLK is your "rebel flag".