You just weren't taught about the violence that occurred, except for Emmett Till and the assassinations. You can go read up on the Battle for Blair Mountain, the Rail Strikes, or Marsha P. Johnson for some very good examples of why violent protest is necessary.
They're saying that MLK was successful because he was a peaceful alternative to violent contemporary protests. Without that backdrop, he would've been less effective.
Okay so what about the Phillipines though? Thats an example of peaceful protests working. Wouldn't we as humans exhaust every peaceful method first if examples show it's effective?