Two corrections
1- While most liberals and even many progressives support gun control, leftists do NOT, for the same reasons you cited. At least there is something farther left and right people can agree on!
2- MLK was not killed by a left wing extremist, he as killed by a right winger...
You're confusing liberals with leftists. Most centrist liberals support gun control. Most folks further left recognize the importance of regular folks having firearms. Also, although this doesn't sound like one, be mindful of FBI frame ups these days. They have made much of their business...