George, Jesus wasn't the only dude to heal the sick and raise the dead, but MLK was not the only one to preach against injustice and bigotry. It's like, Christians are not the only ones who can pray in tongues (buddhists do, hindu's do), but we believe by faith we are doing it on the highest authority and purity.
To take your point further, while a lot of people would agree with your statement/encouragement to "be Christ today", I think few would be able to say "how are we being Martin Luther King today", simply because MLK was a man (righteous though he was) and not God.
How are we being Christ or Christ-like? by healing the sick, raising the dead and preaching against injustice. Some of us are, unfortunately, occasionally at best.