This is certainly nothing new. I'm not sure you can fault someone for honestly wanting to be helpful but I certainly understand your irritation and I wish that people would stick to giving examples from their own experience instead of parroting what they heard somewhere else.

People with little or no experience have been handing out bad advice since the beginning of time and just because you can now do so much more efficently on the internet doesn't mean that will be ending anytime soon.

I think that the best thing to do is if you see someone giving bad advice to simply give them what you consider to be the correct advice. As long as it's done in a polite and civil manner it will generate discussion and you can often find that there are many correct ways to do the same thing. Lively discussions can be a learning experience for everyone. Of course you'll often find people who are just plain stubborn and will not take advice from anybody, but time has a way of weeding those people out.