There have been stories about people stopping to help, and they are kidnapped, raped, or killed too.
Best thing to do is to call 911 and report car seems to be stranded with someone in there, and ask them to send help.
You don't know, when you stop, just how things are going to go, and I'd rather be cautious than dead.
This is just what I was going to say. I grew up with people telling me stories of people who pick up hitchhikers and get murdered, robbed, you name it. This slowly started to include people who needed "help" on the side of the road. I'm a tiny 21 year old girl, it wouldn't be hard to do away with me.
That being said, if I think they look legitimately in need I will stop. Smoke billowing out of hood? Sure. Upside down, or obviously skidded out into the ditch? Yeah, I'll probably stop. I've got mace on my keychain and I usually am carrying a knife. I'll have my phone ready to dial 911 - just in case the person needs help, but just in case I need help too.
I had to steer myself into the ditch one winter night a few years ago. It was 30 below, I was driving to a friend's house in my pajamas (brilliant, right?) and as I took a sharp turn, a pickup came screaming around the bend. In my lane. It was ditch or head on collision, so I took the plunge. Ended up in the ditch, halfway under the boughs of a pine tree. Snow piled up to my windshield and it was so deep I couldn't keep my car running because the exhaust couldn't escape.
Everyone who passed me stopped. A woman got out and practically begged me to come and warm up in her car. Offered to go get her husband to try and haul me out. A tow truck turned around at an intersection to come offer to pull me out (...for a nominal fee). A guy and his son asked if I wanted help. By this time my boyfriend was on his way with his truck and tow chains so I declined their help, but on this dead quiet road at 11 PM where it's not common to see a car for a half hour in the evening, all of the people who passed me stopped and offered help. So, I would disagree when you say chivalry is dead. People need to be cautious nowadays, and I totally respect that, being one of those people myself.