Photos of the Tiananmen Square protest, arguments that Mohammed was not really a prophet of God, arguments that God doesn't exist, and maps that claim that the actual boundary between two countries are on one or the other side of disputed territory, are also illegal in many districts and countries.
Probably it would be bad if the only speech allowed on popular web sites were speech that wasn't illegal anywhere, or illegal in only a few places.
While I can't really speak to this particular objection, it would be patently absurd for Reddit to be required to be compliant with all laws in all countries, that's just inane and a completely losing battle.
If a specific country outside of where Reddit's servers are hosted has a problem with it, then they're welcome to ban it.
Are you sure? I'm on quite a few anime subreddits and they all explicitly state sexualisation of characters that are even canonically adults but have the appearance that someone could mistake as being a minor is disallowed. They are/were so heavy handed about it that there were revolts on a few of the meme subreddits, but nothing was changed as it was global rule changes, not sub specific.
Probably it would be bad if the only speech allowed on popular web sites were speech that wasn't illegal anywhere, or illegal in only a few places.