Another thing to bear in mind was that a large part of the civil rights movement was blacks trying to exercise rights which they theoretically had a legal right to exercise in the 1950s and 1960s - vote in federal elections, travel in integrated interstate buses and use the bus terminal facilities during transfers, attend all-white public schools which the Brown decision had forbid in 1954 etc. So this was the government using its intelligence powers to secretly persecute people who were trying to non-violently exercise the rights they technically had under the law.
Who know what political uses the information stored in the Utah Data Center will be used for in the future?
The case against King was a little more specific than that, though still not a reasonable basis for suspicion: One of his close associates had historical ties to the US communist party.
It was such a weak case that Hoover had to really push on LBJ to let him go after King so aggressively, and probably reflected cryptic racism as much as his fear of communism.
All governments to varying degrees seem to operate with a number of hidden imperatives, with one being "maintain the status quo." There will always be some within the government bureaucracy who see anything that deviates from the status quo of their host society as criminal or an enemy.
I get that. And that, compared to the terrorism threat, communism was a real issue. It didn't look like we were winning, and there really were people on foreign government's payroll in the US. The problem is the ends didn't justify the means, because they were wrong.
I do consider myself patriotic, but we have to fess up when we get things so wrong.
Civil Rights Movement -> Destabilizing Effect on American Culture -> Probably a Communist Plot -> Civil Rights Movement is the Enemy