Watching it now for the 100th time ----
Does ANYONE really believe that at that time in the west, especially on the border
That anyone would be frightened by the statement the Doc made to the bad guy
" Luke if you go outside with that shotgun I'll have you indicted for murder "
The kids plan was to kill and run to Mexico -- Premeditated -- Indictable
Luke being told the Kid is coming to kill him, for whatever reason, would be acting in self defense