The first is that if you have a good reason to think something is wrong, the fact that it happened in another country or culture isn't a reason not to say so. I'm happy to put the shoe on the other foot. If there are practices in my country (the US) that someone from elsewhere has reason to think are wrong (and I'm sure there are), I wouldn't think it was arrogant to offer up the criticism. I agree that there are serious questions about the history of Western behavior toward other countries, but we can distinguish the issues at least conceptually. For example: I'm quite willing to say that it's wrong for a country to execute people for being homosexual, whether or not the West has things to answer for in how it has dealt with that country. There may be more or less arrogant ways of making the point, but that doesn't make the criticism illegitimate or inappropriate.
The second point is that if it's wrong to execute people for drug trafficking, then the traffickers don't deserve to be executed for it, even if they knew what the penalty was. Go back to the case just discussed: whatever the law may be, and however well aware someone was of it, no one deserves to be executed for having a homosexual relationship. That means that the blame doesn't stop with the lawbreaker. The country with the bad laws shares the blame. And if the law is egregious enough (as I'd say it is in the case of executing homosexual people), then I'm not willing to put any of the moral blame on the victim.