Here's another angle. Perhaps the stranded individual is vulnerable and if you don't stop, the next person that stops will be an opportunistic violent person out to do harm...
Growing up, there were several times my mother was stranded and some nice fella helped to change a tire or jump a battery or otherwise help. She was a frail woman, and desperately vulnerable. I shudder to think if Mr. Hero didn't come along when he did to help, the next car may have been Mr. Villain. I was a kid with her a few times, and we were in desperate need of assistance. Times were different for certain. But in those days, there were no cell phones or roadside assistance, and concealed carry permits were quite rare. I have hitchhiked. I have picked up hitchhikers. I have helped stranded motorists. Never had an issue.
As to hitchhikers, I've hitched and picked up hitchers probably a dozen times. Some funny stories.
* When I was about 15, in my small town, I was picked up by a guy who told me he was on his way to the nudist colony nearby. I had no idea it existed. He was weird, but harmless.
* I was living in Scotland and picked up by all sorts of amazingly nice people, including a family that drove me several hours to my destination and gave me several bottles of wine from their collection they had purchased earlier that day.
* I picked up a stranded motorist on I-80 during winter somewhere in Nebraska. Temps were dangerously low. It was late at night, and the man was desperate. I drove him 30 or so miles to the nearest town. I've rarely met a more appreciative man in my life. He offered me a lot of money, which I declined, and ultimately forced me to take at least $10 which I accepted to not be rude.
* I was walking and stranded during winter in the mountains of Colorado. Long story short, I was under dressed and the walk was much further than I expected. It was dark on a desolate road. Thank the Lord I got a ride, as I could have found myself desperate in short order.
* I picked up an apparently homeless combat veteran (man in his 20s) and his dog - clearly PTSD afflicted - off the interstate onramp. Drove him probably 10 miles or so, and bought him and his dog some McDonalds for breakfast. He was a really nice but troubled young man.
* I know there have been many other examples of how I've helped give people rides places, and know I've been helped terrifically as well, over the years.... never had any issues. But one must be guarded and I would never suggest breaking the law!!!!
Yes times change. While nationally violent crime may be lower, there are really twisted and violent people in the nation, in every town, in every state. Criminals can travel quite easy and motivations for crime are nearly endless (drugs, money, property, ID theft, sex assault, etc.). Criminals can be quite sophisticated in their tactics, and can learn from others on the web or in jails.
Times changing also means that more people are armed now than ever before. You. Me. Him. Her. Guns are quite common in society, which is a good thing overall. But bad people do have them.
Times changing also means cell phones and roadside assistance is available. Modern cars are so complex that most would be of little help other than a phone call and some company until roadside arrives or a ride to the next town. Often offering to send help or make a call for someone is about the most that can be done.
Times changing also means that a person like me realizes there is danger in offering a ride to a stranger - carjacking, allegations of sex assault by a female, and even being attacked or murdered. Too many crime shows where a person invites a stranger into his life (car, home, etc.) and that decision turns out to be a bad one.
Now, my practice might be to weigh each case individually based on perceived risk. I might drive by offering zero help, I might offer to make a phone call for someone, offer a jumper cable assistance, offer to help change a flat, or offer a ride... it just depends.
It is/would be a shame if we lived under such fear and lack of 'community' that we cannot offer help to others. As I said, I've been on both sides of that coin. I know I've helped many people in great ways on the side of the road. Once I was the first vehicle on a desolate curve and came upon a large truck that had rolled many times, and the driver was badly injured and had crawled away. This was before I had a cell phone but the driver had one. He couldn't operate it due to his injuries, so I used it and called 911. Other times I've helped change tires or jump batteries for very appreciative helpless people.
I feel that we have a duty as humans to help when we can... but of course you need to be smart about it. One must always go in with eyes wide open and be ready for an ambush. Don't turn your back, get into a strangers vehicle, hand over your keys, etc.
in a median/part of a 2 lane road(urban area street). I slowed down to ask if the vehicle occupant(a female 45-50 years old, drunk or high on drugs) if she needed help. 
