The secret service is under the DHS, not the CIA or FBI, which have been the organizations criticized by RFK, and JFK for that matter.

The DHS didn't even exist back then, the SS was absorbed into it some time after it was created in 2002.

Regardless, one can want the usual protections given and needed and also hold the belief that some agencies are too powerful and corrupt and need to be broken up. (like breaking up the DHS and making the SS it's own entity)