I can empathize, OP. I tend to *want* to do this all the time.
The thing is, your respect for the English language isn't something that's easily perceivable for most folks. What you see as simple care and consideration, they'll understandably see as pedantry.
Live and let live. People are generally more open to the idea of being corrected on paper than in person. As a rule, I try and correct other people if doing so pulls them out of a bind; not otherwise. Say, a loved one's updating their resume, and you spot a formatting mistake that makes their document less appealing to the average employer. That or, say, typos.
Then yeah, you're justified in offering corrections. If you're just doing it in the middle of a casual conversation, though? That's a jerk move. Never correct someone if they haven't asked for it. That's the long and short of it.