(Mild spoilers -- but why try to answer if you have not read the book?) While there is no question that the gang indulges often in violence with minimal or literally zero provocation (the puppy episode is so pointless and evil), there are a few cases where Glanton actually behaves fairly decently. For example, when they encounter the men trapped in the abandoned fort (with the snake-bitten horse), while Glanton rejects their offer to join the gang without even bothering to say, "no", he does leave them valuable lead, powder and primers.
Two other cases are allowing the circus performers to travel with his gang. This might simply be what people did in those dangerous days, even bad guys, if it was no skin of their noses. He might also have wanted them to provide entertainment.
More puzzling are taking the Bell brothers. They do charge money (I think) but Bell makes it clear that he has far less than the 100 bucks that Glanton was asking for and even if he did have the full 100, were they that hard up for money that they would want the burden of traveling necessarily slowly with the handicapped brother being in a cage -- this really makes no sense to me. He could have planned to exploit them in some fashion, but I can't think what that may be. The really horrible idea is Glanton, just for the heck of it, planned on abandoning the two in the wilderness, but there is no evidence. The Judge of course may have had plans for the imbecile and influenced Glanton to take them along.
Somewhat similar are the Mexicans bandits (not sure what they were) that the Kid and the wounded man encounter when they are dying of thirst. These men are known to the Kid to be murderers, part of the Indians who killed so many of his fellow mercenaries days before -- he recognizes the Captain's horse. Nonetheless, the not only do not kill the Kid and his companion, but they give them both water that probably at that point saved their lives. They do no more; they do not leave them with water and they sure do not offer to give them a ride or come back -- indeed, the lead bandit is almost certainly aware that they will be dead in a day or so, as they would have been had they not encountered the donkey cart. But he does let them drink when they themselves were probably short on water and, again, they do not kill them even though they almost certainly know that the two men were part of the mercenaries that they had helped slaughter? (I think this is implied that they were working with the Indians.)