(1) King had to publicly reject Communism in 1957. Too many people associated with his movement were out-and-out Reds. In order to avoid trouble he made these statements.
I will add that in 1959 Fidel Castro made similar statements himself - and we know how that turned out.
(2) If King really despised Communism for its "moral relativism" why did he continue to associate with Communists like Bayard Rustin?
There are only three possible reasons: (a) He was a Communist posing as a non-Communist; (b) he was too stupid to realize that Rustin was a vocal Communist (doubtful) or (c) he was willing to use Communists to help in his movement while ignoring the fact that they were fighting against everything he claimed to believe in. If the latter were the case, then he stands as a proponent of the same moral relativism that he accused the Communists of practicing.
(3) The "Poor People's Movement" in its rhetoric and in its platform was identical with Bolshevik ideology.
(4) He talks about the divine order and God - but his sermons and speeches are famously devoid of any supernatural content - in all of King's work the Kingdom of God is here and now and is found in the form of creature comforts and political power. The supernatural is nonexistent for King except as a source of rhetorical fuel for his extremely secular fire.
If Castro ever denounced the philosophical and applied basis of even theoretical communism is even close to the enthusiastic and thoughtful terms as King did, I would be curious to see your reference.
If King was a commie before 1956, he was certainly a strange one. He endorsed Ike in 1956 and often praised Vice President Nixon's civil rights record, two actions very much contrary the party line. I can provide the references if you wish.
King specifically and at length denied that he was a social gospelite in Stride for Freedom. He specifically criticized the Social Gospel overemphasis on worldly things and its view that society could be perfected.
Read the Collected Writings of King and you will find many sermons which stress the importance of spirituality. As Baptists go, King was something of a moderate doctrinally....but not a securalist or quasi-Unitarian. One of his most famous sermons, which discussed the dangers of avoiding churches which either "burn up" or "freeze up," stressed the need for churches to maintain spirituality while at the same tackling have application to the lives of parishioners.
Abernathy, even after he endorsed and campaigned for Reagan in 1980 and exposed King's affairs, always rejected the charge that King had been a commie. By endorsing Reagan, and discussing King's sexual habits, btw, Abernathy had been disowned by the civil rights establishment, and thus no incentive to cover up for King.
Charles Evers, who knew King well, has also rejected the Commie charge. King's niece Alveda, disowned by the family because of her support for vouchers, criticism of gays, and support for Bush, also defends her uncle on this issue. The same is true (I believe) with James Meredith who even endorsed David Duke and thus would have no reason to cover for King. Can you name *anyone* associated with King who now claims he was a commie?
Bayard Rustin had been a commie (so was Eugene Genovese and, so I remember, Irving Kristol) but had long since broken with the party and denounced it on many....many occasions. Long before he died, Rustin had become a died-in-the wool social Democrat. Hence, Rustin was closely associated with Norman Thomas, a social democrat who zealously avoided communist connections. I wouldn't call the Poor People's Movement "Bolshevik" but it was certainly a crazy, leftist, and extreme movement of moochers. Having said that, it was near the end of King's career. It was also during the late 1960s when a lot of otherwise sane people went crazy. King was a very different man in 1967 than he had been in 1957 or 1963.
Though he was a social democrat with pacifist inclinations, he was started to work closely with neo-cons in the 1970s. He condemned the PLO as terrorists, organized public campaigns against Soviet persecution of the Jews, spoke out against the Soviet Union's use of Cuban troops in Africa, and became a spokesman for the anti-Communist Freedom House which supported the view "that no matter the alternative was, Soviet domination could be worse." Daniel Levine, Bayard Rustin and the Civil Rights Movement (Rutgers University Press, 2000), 20, 237.