I've been quilting so long and have finally learned how to smile and nod and say "thanks for letting me know" in an annoyingly perky voice when I get unsolicited quilting advice. I suspect a lot of people think I'm a dolt!
There are "police" in every field and hobby. My husband is a fly fisherman and he's been told he doesn't know what he's doing for 40 years. He's got the "smile and nod" response down. Actually, I think I learned it from him!
I believe that people who always "know better" are insecure about their own skill set, or just cranky and controlling in all aspects of their lives. I refuse to let them bother me, and there's no point in arguing with them because they will never admit they're wrong about anything. If you let them bother you, they win.