We'll, regarding Japan, they sort of did this for a couple centuries and as a sovereign state they were entitled to do it, provided they can bear the consequences.

It wasn't until the USA sent a warship into the harbour and said "At least open yourself up to trade or well make things very unpleasant for you" that they allowed any foreigners in at all.

Even now, it is incredibly hard to emigrate permanently to Japan as a non citizen unless you have some sort of ancestry I imagine. In many countries you cannot own land as a foreigner.

It's "okay" because they are a sovereign state and can make whatever laws they feel like and short of going to war or applying sanctions noone can do shit about it. Same as Indonesia can make pre marital sex illegal, or outlaw being gay.

Countries don't really operate on ethics the same way individuals do is my short answer.