Be smart, be aware, and you don't need to worry very much about people, but they can be a risk factor depending on where you go and what you're doing.
ShemSeger's answer sums up my general impression of the types of crimes/interactions that I would be most concerned about, ie vandalism and/or "territorial" disputes. My comment that you referenced was mostly to stress:
- That animal encounters where the animal is likely to attack you are rare.
- It is often the things we don't worry about, other people being one of them, that can get us into trouble.
People go into the wilderness for all kinds of reasons, so I think it stands to reason that all kinds of people will go into the wilderness. In general the proportion of honest citizens to criminals you meet on any given day, in the city, heavily balances toward the honest citizens (unless you're some kind of criminal ring leader). That means that I would expect that the vast majority of people you meet in the wilderness are good, honest people, but there will invariably be some criminals. Also, the wilderness offers reduced oversight by law enforcement so it will attract a certain kind of criminal.
To a certain degree criminality in the wilderness will be affected by what type of crimes you're talking about. Does underage drinking count? Does negligence leading to a major wildfire count? Does intentional arson count? etc... There are some crimes like attempted/successful homicide and/or sexual assault that clearly count so I'll highlight some of those statistics.
In rural Northern California I know Mexican Cartels, some Native Americans, and some locals have been known to grow marijuana illegally on Forest Service land. My brother-in-law has been shot at multiple times while performing drug interdiction duties. My father has been warned off land by people in no uncertain terms while hunting. Furthermore he has seen bowls of anti-freeze scattered about the woods to kill any animals that might be inclined to forage on the illegal crops. This is a danger, but mostly to hunters because recreational hikers will rarely venture far enough off the beaten path.
Full disclosure I'm not a woman, nor a particularly attractive man. I don't worry about sexual assault but according to this website there is an above average risk of sexual assault in Yosemite National Park (159 vs national average of 100). They also give a risk of 294 vs the national average of 100 for physical assault in YNP. I don't know if those numbers are accurate, but if they are then people are clearly a threat.
Another website1 that may or may not be accurate states this about YNP (danger rating2 10.3):
While the three women hikers murdered outside park boundaries last year made headlines, theft from park hotel rooms is more common.
Here is what they say about Everglades (danger rating 10.8):
It's not the notorious gators that pose the biggest hazards here -- there has been only one unprovoked attack in the last 53 years -- it's car break-ins. Indeed, the park has an unusually high number of larcenies per visitor.
According to that website Lake Mead, NV3 has the "highest rate of serious crime of the parks we looked at" and has a danger rating of 13.6.
In closing here is a report from ABC News:
"Just about any type of crime that goes on in any urban environment happens out here," said Dale Antonich, chief ranger at the Lake Mead National Recreation Area, located in Nevada and Arizona.
"We've had rapes, we've had murders in the park, we've had bodies dumped in the park," Antonich said.
And yet, as troubling as urban crime may be, it is nothing compared to the lawlessness we found in parks along the nation's borders.
The rangers at Organ Pipe wear camouflage and bulletproof vests, and carry assault rifles. They look like special forces soldiers on patrol in Iraq, but they are park rangers on duty in what rangers believe is the most dangerous park in America.
1: This data/page appears to be ~20 years old.
2: Incidents per 100k visitors including crime and accidents.
3: Note this is relevant to the area that my comment was placed.