Cultural Relativism is the philosophical view that one culture cannot legitimately criticize another culture, because there is no objective truth about morality. It's like if America like Coca-Cola we can't criticize Canada for liking Pepsi because, it's a matter of opinion. So, in reality, if UK wanted to criticize America for still having the death penalty if they were cultural relativists they would say, "That's just what America thinks is right."
I don't know about three but one consequence is that if we were cultural relativists back in the 1940s then we would have let Hitler take over the world, because we wouldn't be able to legitimately question Germany's use of mass genocide because that's just what Germany thought was right. The same could apply to China's violation of human rights (which are mostly ignored because we love our cheap Wal-Mart crap). A cultural relativist would say, "That's just how China does it. They probably don't like a lot of things we do like the war in Iraq and the disproportionate pollution per population the US is responsible for." The cultural relativist's biggest flaw, if taken too seriously, is that he would ignore and he would, if not support, then at least tolerate massive human rights violations.
It could be pretty persuasive if done about little things like eating dung beetles and monkey brains. That's a situation where Cultural relativism is probably a good thing, but as the stakes increase it loses its appeal.