I always stop people to correct them and let them know they're spreading B.S./misinformation. Everyone should always correct people if they know they're speaking rubbish.
If I corrected and spent time arguing with every fucking moron who said something stupid, I wouldn't get a lick of work done, or any sleep, and I'd be in a constant rage 24/7. At some point you have to decide where to pick your fights and when to let morons be morons.