Never. Most people have no idea it's bad, it's way too easy for kids to access porn and start getting used to it early, and most parents are terrible at teaching their kids about sex and relationships even in the most basic and general terms, let alone about hardcore porn being bad for you.
Consider smoking cigarettes, a vice which became extremely popular in the 20th century, pushed worldwide to this day by large corporations making insane profits, just like porn. For decades people had no idea smoking was a dangerous habit, some even believed it was good for your health, just like porn. After studies came out in the second half of the century showing the truth, there has been a push to stop people from smoking -- unlike porn, with which we haven't even gotten to this point yet. Now you have governments mandating labels showing disgusting imagery saying smoking will kill you; you have tobacco products being taxed to hell; you have doctors telling you to stop smoking; anti-smoking legislation prohibiting smoking in various places; sob stories about cancer and health awareness all over the internet and media; you have people telling you it smells and bothers them, and this has all been going on for at least 20 years as culture has been shifting. Yet people still smoke. Some smokers even seem to get extra enjoyment out of spite for the people nagging them about it. There are new forms of smoking (vapes, e-cigs) being developed.
Do you think smoking is ever going away? I think the answer is an obvious no, and the same goes for porn.