Y'know, that used to be my policy as well, but I've found that every single time I've stopped to help people they react with some flavor of hostility to me. I dunno, maybe it's my manner.

The last time I helped someone (after which I resolved to never again, unless they were in danger) was when I helped a woman put the chain on her kid's rusted-a** BMX-clone bike. The chain kept slipping because the rear axle nuts were fused to the bolts and the chain couldn't be tightened. The chain was literally rusted solid at a couple of pivots (where pivots wouldn't move any longer). I helped her to get it back on, and gently told her,
"Y'know, if you just spray a little WD-40 on that pretty regularly, it'll help you a lot, and will be less dangerous to ride on."
She stared me down, told her kid to get on the bike, and [as she rode off] said to me, "We didn't really need your help, anyway."

F*** that noise. From now on, unless I see someone bleeding or crying, I just keep riding.