There are lots of vices and tasks that adults can usually handle but minors may not. Alcohol, tobacco, drugs (in as far as these are legal in a given jurisdiction), voting, operating heavy machinery, driving cars…
In Japan sexually explicit comics are strictly 18+, clearly marked as such, and are sold as you would sell liquor or cigarettes. Making sure children don't have access to these is a matter of public awareness and parental guidance — it seems to work pretty well there.
> I know people who have been messed up when they were very young and found it.
Messed up from lolicon (i.e., Japanese comics featuring minors in sexually evocative situations) or messed from access to porn in general (or even actual child pornography)?
As I said explicitly, messed up from freely available lolicon comics and content on the internet. The vices you list all require physical exchanges with others or would usually be noticed by adults nearby, and so they aren't really comparable.
True, unmonitored access to the internet can expose minors to things that can have an adverse effect on their psyche. But let's limit ourselves to freely available online content. Singling out lolicon (or any other form of drawn porn) seems dangerously inconsistent to me.
Violence, hate speech, gore, (adult) porn; even written fantasies containing content that may stimulate forms of destructive behaviour — the list is endless! Either you shield children from all of it (which is sensible for young children, but not tenable for teenagers) or you educate, guide, train, and accompany your child as they learn to handle an ever increasing amount of freedom. Parenting and education are key here, not banning everything that may harm a child's mind.
In Japan sexually explicit comics are strictly 18+, clearly marked as such, and are sold as you would sell liquor or cigarettes. Making sure children don't have access to these is a matter of public awareness and parental guidance — it seems to work pretty well there.
> I know people who have been messed up when they were very young and found it.
Messed up from lolicon (i.e., Japanese comics featuring minors in sexually evocative situations) or messed from access to porn in general (or even actual child pornography)?