Heavily sampling the Buffalo Springfield classic "For What It's Worth", Chuck D and Flavor Flav bring us a song on the slow tip. From the 1998 movie of the same name, the song represented a comeback of sorts. Sure, it wasn't as angry sounding as earlier PE tunes, but lyrically, it still packed a bite.
And yes, that is Stephen Stills - of Crosby, Still & Nash (and Young), and, of course, Buffalo Springfield - reprising his vocal in this video and on the single.
In contrast, here is one of their earlier songs - "Bring The Noise" - which has a lot more energy..... and a lot of anger. This is the original version, with just Chuck D and Flavor Flav on the vocals.... mostly Chuck D, but Flav is so full of energy and amped up the volume.
A lot of people see Flavor Flav as just a goofy guy. He is far more than that. He was the energy of the group - a yin to the yang that was Chuck D's intelligent hip hop.
Of course, once Anthrax got involved, the volume went waaaaaaaaay up. This is the version most people know. It's not bad, but it isn't my favorite version. The collaboration grew out of the New York city metal and hip hop scenes, which were closer than a lot of people thought they were.... I mean, until Aerosmith met Run DMC.... but that's a story for another day.