MLK did not protest for support or to display their convictions - it was done to fight the legal system. They staged events to get arrested and charged for crimes relating to segregation and rights denied to them - then the lawyers came into play. They challenged the constitutionality of the laws, over and over. They overwhelmed the courts so much it hampered their ability to function. They lost plenty, but every small win persisted and chipped the laws down little by little

The black Panthers were an implied threat - "were watching, and we're armed too. We'll play by the rules if you do". They primarily upheld the rule of law, by limiting extra-legal punitive crackdowns on Black communities. There was some less reactive violence, but that wasn't their purpose

Civil disobedience wasn't peaceful for optics, it was a third path strategy to turn the system against itself. Returning the violence would defeat the primary purpose, because it would weaken the legal challenge

All that being said, the two organizations were separate wings of the same movement. They both played important roles, one faught for fair laws, the other for fair application of the law. Their methods were incompatible though, so they needed strong separation