First, the original poster should be someone who will be willing to engage with you. If the post is coming from someone who is very clearly making inflammatory statements with the intent to get a rise out of the community, it is unlikely that responding to them on that post will do you or anyone else any good. If anything, you will end up encouraging their irresponsible behavior. If you still feel the need to publicly disagree with them, consider doing so at a different venue, such as your own blog. This gives you the ability to make an important point without fanning the flames of conflict and driving traffic to the offender's writing space.

Second, you should only engage in the public debate if you are well armed with information. For example, if someone is doling out incorrect health advice, and you happen to be a doctor specializing in the area in question, disagreeing is not only a healthy choice for building your reputation, but nearly a moral responsibility. If you are disagreeing with someone based on your own experiences, you can still disagree publicly, but you should cite another expert to back up the experiences you're referencing, or preface your opinion with its limitations.

Third, you should only disagree if you can do so coolly, respectfully and constructively. We all have things in life that we're passionate about. However, if your passion easily turns into rage, then it might be best to abstain from commenting, as digital temper tantrums are no more appealing than physical ones.

Finally, you should be willing to continue the debate beyond your initial post. Making one contrary comment is commenting just to comment, which really limits the utility of commenting as a whole. Be willing to respond to the comments made by the original poster and other commenters. Not only does this make you a responsible commenter, but it helps to foster a healthy and active community conversation.

Now you know when to comment- but how should you execute your disagreement? More on that later today. Check back at the blog for more information!