Words don't need to be said; words don't have needs. People sometimes could benefit from hearing words. But if you're going to be a jerk about it, then people generally aren't going to listen. Ergo, no benefit.

In this case, though, I don't think stating the obvious was anything that the original poster needed to hear. You were responding to something where he already said that he was "a dummy" and will do it differently next time.

And I think your accusation of laziness is... unevidenced. He's a college sophomore at a selective school, he's studying half-way around the world from home, he has a number of neat projects on his blog, and decided to make a cross-country trip over Thanksgiving break. And in a follow-up to a theft, he took the time to post something to help other US visitors avoid thefts in the future. That doesn't look lazy to me.