Maybe weirdest thing about Sam isn't his love of violence and his general dedication to mayhem. It's really that London and Mac think he's a super guy. London, in fact, gets all sentimental about him after Sam sets the Hunter house fire:
"I got a feelin' he ain't comin' back. Funny how you can get to like a mean man like that. Always got his chin stuck out, lookin' for trouble." (225)
In his "lookin' for trouble," Sam is a whole lot like Joy. Just like the older man, Sam has seen a lot of violence and oppression in his life. He explains to the picketers, for example, that he was with the longshoremen in San Francisco when things went down on Bloody Thursday.
This traumatic event galvanizes Sam and fuels the anger he feels when he meets more injustice in the orchards.
Despite his wildness, Sam makes a good impression on the leaders of the strike. He's pretty much willing to do anything for them, including putting his life on the line for the team—like when he burns Hunter's house without implicating the strikers.
London likes him even more after that, even though the act mystifies him. As Sam starts out on his self-appointed arson mission, London, despite having punched Sam in the face earlier, tells him that he's a good man and that he hopes to see him again sometime.
Despite London's warm fuzzies for Sam, there's something uncontained and dangerous in him. It stems from the dissatisfaction of his working life and the anger he experienced when he witnessed the disaster back in SF.
We know that the Bloody Thursday massacres are at the heart of Sam's manic energy because he mentions it constantly. There's a ferocity bubbling just under the surface for anything that reminds him of his epic experience with the longshoremen.
When Bolter tries to pass off violence against the orchard workers as necessary to keep public order, Sam loses it:
"And you get order by shootin' our men from windows, you yellow bastard. And in 'Frisco you got order by ridin' down women. An' the newspapers says, 'This mornin' a striker was killed when he threw himself on a bayonet.'" (194)
Sam may be a man of one theme, but the comparisons between the two situations are not inappropriate. He can see that Bolter and the landowners don't think of the workers as human; to these bigwigs, the workers are not even part of the general public that deserves peace and order.
The futility of kicking against the machine of systemic oppression makes Sam the most frustrated and volatile character in the work. But don't worry, Mac says. Sam has seen it all before and knows what's coming, what's needed to further the cause:
"Somebody'll kill him sometime, like that little guy Joy. [...] It's almost sure, but it doesn't make any difference." (225)
What's more, Sam is looking for it.