Joe put out a statement Wednesday after last week's news that assassin Sirhan Sirhan was getting out of prison after 53 years. It's pretty scathing ... he says flatly, Sirhan doesn't deserve it.

He writes, "I echo the anger and heartache of my father, a majority of his siblings, and my grandmother at the California Parole Board's recent recommendation. For our family, there has been no apology, no acceptance of responsibility, and no remorse."

JKIII adds this ... "For our country, there has been no justification for letting the perpetrator of one of our most devastating political assassinations walk free."

Joe goes on to explain the U.S. cannot accept violence as an answer to political disagreement ... which he suggests is what led to Sirhan killing Bobby all those years ago. He adds he's all for rehabilitation of criminals, but for those who skirt responsibility -- like Sirhan  -- Joe says "there should be no accommodation."

It's a pretty fierce take on the strong likelihood that the 77-year-old will walk free soon. He's also standing against Robert F. Kennedy Jr. and Douglas Kennedy -- two of RFK's sons who've come out in support of SS's release.