... Is that they aren't always murder-hobos.
The complaint that circulates periodically is that D&D adventuring parties are basically just bands of homeless sociopaths breaking into the homes of helpless orcs and goblins and killing them for money. Now, I've said before that there are problems with thinking of the goblin treasure and goblin-infested ruins as being their property, but let's leave that aside.
What's more serious is that some people seem to apply the "murder-hobo" label to any kind of character who kills and then receives a reward. The knight who slays the dragon to save a village, or slays the evil sorcerer to rescue a princess. The rough mercenaries hired to pull a "Magnificent Seven" and fight off marauding bandits. And so on.
It's one thing to call someone a "murder-hobo" if their motivation seems to be purely financial and amoral. It's another thing to ignore any motivation whatsoever and re-interpret a person's actions in purely financial terms. Adventurers who are knights errant, or demon hunters, or a borderland militia, aren't just acting out of greed; they have a moral system, even if you can't see it or agree with it.