Why would the government spend resources on spying on feminist groups and/or black people social clubs? They pose literally zero danger to the interests of the ruling class?

Respectfully, that take is naive as fuck. Considering the political climate then (and even now), it's not hard to see how groups of citizens banding together for collective actions can easily disrupt the gravy train of the money class. Look at how quickly shit gets done in places like France when they have a general strike.

A mass of citizens banding together will ALWAYS be a threat to the ruling class. Because the ruling class only rules as long as the population is willing to let them rule, because their rule requires the citizenry to enforce and uphold the system.