The original point was that if a country is doing something now, that can be an excuse for another country doing the same thing now.
If you want to extend your excuse to "a country did something bad 50 / 100 / 500 / 1000 years ago (and later regretted it)" then you need to provide extra reasoning for why that still works as an excuse for what a country is doing now.
Edit: I'm guessing from the downvotes that I didn't make my comment clear enough (or I didn't understand the comment I was responding to). My intent was to point out the logical gap in an argument that could be seen as justifying China's genocidal policies.
If you want to extend your excuse to "a country did something bad 50 / 100 / 500 / 1000 years ago (and later regretted it)" then you need to provide extra reasoning for why that still works as an excuse for what a country is doing now.
Edit: I'm guessing from the downvotes that I didn't make my comment clear enough (or I didn't understand the comment I was responding to). My intent was to point out the logical gap in an argument that could be seen as justifying China's genocidal policies.