Why do my parents tell me it is morally wrong to have a "hickey" or love bite on
From what I recall (and I'm recalling going to a US highschool way back in the 20th century), there's quite a bit to the semiotics of hickeys. The bruise says something--to you personally, but also to the world (if you hair is mobile). It broadcasts "I have a boyfriend and we're intimate," but it also hints at sex to the point of hurting. Maybe your parents have concerns about the broadcasting, or about "to the point of hurting." Maybe they're wondering "what next?" Maybe... Well, you could speculate endlessly. There's no way to know without asking them. You might discover that they're worried not so much about morality but about your emotional and physical health.