The problem is not code. The problem is that no one wants to take this responsibility. Every one wants to talk about supportive they are on sex positivity until some men in uniform knocks on their doors because they are running a website that is available for minors all around the world.
Also, I don’t even want to get in the discussion of “sex positivity” being associated with “easily available porn”. Like you said, porn is easy to find and I really doubt that the someone who is savvy enough to use Lemmy would have trouble to know where it is.
Of course it does have an effect, but there is a difference between “can be found” and “should be encouraged to be treated on equal footing as any other community forum”.
Much like “absolute freedom of speech” platforms that inevitably end up catering to people who want to say only repulsive things without repercussion, what do you think will happen if you create an online space and put a big billboard saying “here you will always be free to share your NSFW content”?
Content discovery of porn should not be as easy and it should not be trivialized under the pretense of “sex positivity”. One can have an absolutely open mind about sex and sexuality while still wanting to keep a clear boundary of when/how/whom to talk about it.