Yes, you read the last part right.
First, JFK was shot by Lee Harvey Oswald, acting alone.
Second, a man who actively supported the overthrow of the president of South Vietnam for not being anti-Viet Cong enough, then professing to be mortified over Diem's murder, must be considered a hypocrite of high rank even among the 43 men to occupy the Oval Office so far.
Let's look at the Kennedy reality.
1. He got "rolled" by Khruschev in Vienna in 1961, perhaps in part because Dr. Max Jacobsen's amphetamines had started wearing off.
2. That, combined with the Bay of Pigs failure, surely led to his "tough on Cuba" strategy, which wasn't that tough.
2A. By not having LBJ involved in all ExComm meetings, he let Johnson think he was tougher on Cuba (i.e., that missiles weren't swapped) than was true; hence, Jack Kennedy contributed to wider war in Vietnam that way alone.
3. The Diem assassination shows he would have upped the military pressure in Nam through the 1964 election at least, leaving either him or the unlikely Goldwater to continue expand the war.
4. How much JFK would have expanded the war is open to reasonable debate; that he would have expanded it to some degree is not.
5. The best think JFK ever did domestically for civil rights was to get himself killed, so LBJ had a martyr to spur Congress into action. Go all the way back to 1960. Kennedy was as politically scared to call Martin Luther King in jail as was Nixon. Eventually, Harris Wofford picked up the phone and forced the issue.
6. Sidebar to this: Kennedy is the only president to deliver an inaugural address without a single word of comment on domestic policy. Beyond being the arch Cold Warrior, he was arguably an arch imperialist, indirect American style.
7. The various conspiracy theorists who wander Dealey Plaza are rightfully scorned for the degree of their detachment from reality; the worshipers at the Shrine of Camelot are not. Why not?
UPDATE, Nov. 26: Ross Douthat, in a column I largely endorse, weighs in on both the Camelot myth and Stephen King's new time-travel novel about the assassination. Frank Rich tries to have his cake and eat it, too, noting (per Douthat) that he wasn't that liberal, but replaying the old canard that right-wing hate killed Kennedy. No, as Douthat puts it, Oswald was, really, the Jared Loughner of 1963. William Manchester gets that wrong, too. Dallas was a "nexus" only in that Oswald lived there, not because of any atmosphere of right-wing hate.