Deke Thornton (Robert Ryan) repeatedly calls the members of his posse "gutter trash" and the like. Well, what is he? A freed-on-condition prisoner who was once a member of the very outlaw scum he's chasing. At least the posse members -- lowlifes that they may be -- are on the right side of the law.
shareTo be fair, even though the bounty hunters were on the side of the law, they were such horrible, loathesome people that they made the real outlaws, The Wild Bunch, look like knights in shining armor.
I think Thornton was talking more about personal characteristics and habits than abiding by the law when he called the posse "gutter trash".
Also, you have to remember that this movie came out duing the "anti-hero" trend of the late 60s and the 70s. Everyone, especially the youthful counterculture, viewed "the system" as corrupt, and those who fought against it as virtuous.