A lot can change over a decades time. I hope and believe that porn will eventually be a lot more restricted than it is today, as the societal downsides become more and more apparent.
It's starting to look like removing some of the sexual morals that societies had used for hundreds of years is a classic Chesterton's fence style problem. Progressives didn't understand the good effects of some puritan policies and decided to throw it all out because it got in the way of them feeling good right now.
Limiting personal freedoms to satisfy old religious beliefs (some of which used to serve useful purposes) makes very little sense nowadays, especially that we have much much much better ways to get much better outcomes with regards to those purposes. (Eg. avoiding genetic defects due to incest, keeping communities growing to have enough people to replace those who are lost due to famines, disease, war, accidents.)
Cultures that have these rules and restrictions seem to be growing via positive birth rates while cultures that dont are stagnating and not growing and seem to be actively committing cultural suicide. So its not obvious to me which path evolutionary processes will choose to win out in the long run.
These two things are hugely different. Kids can and do regularly begin viewing porn right at puberty. There was never such easy access to sexual simulation even with prostitutes. You also cannot photoshop a real life prostitute, or browse around for the most attractive one in the world. Every additional prostitute you are with is an extra price, whereas each additional porn star is free; it naturally leads to needing huge amounts of stimulation that's incredibly hard to get in real life unless you own a harem. And even then if you're into the really hard-core stuff you'd have a hard time finding willing participants.
Porn and prostitution are totally different
not sure, but in the greater picture of overpopulation, porn seems to be a cheap and effective measure compared to medical/physical alternatives.
Source that we are overpopulated? We can shrink the population and still pollute irresponsibly. In the past when the population was smaller we certainly managed to ruin plenty. And we aren't running out of land or food either.