We teach our kids that what they put on the internet now can and will be used against them in the future.
2009-2012 is not shockingly long ago. The internet was not new and the idea that what you posted would be available forever was not new either.
James Gunn made stupid decisions when he was younger. Worse, he made those stupid decisions in a public place with a long history and plenty of past and future witnesses. Now those decisions have come back to bite him in the ass.
That's life, and this isn't new because of the internet.