There's no fallacy. You are okay with countries killing people who leave a certain religion as long such laws have popular support. In effect you are okay with, or at least indifferent to, legalised religious persecution in foreign countries, because hey, it's their culture right? And hey, who are you to judge others who have different world-views to yours? Not much of a stretch to ask if you'd be okay with or indifferent to other countries legalising enslavement under certain circumstances if it had popular support?
Though I don't suppose I should expect anything more than a vapid dismissal wrapped in a poor attempt at wit.