Well, no, rape is not just a forceful rape, because the law says that minors up to some age are not capable of making decisions on who they have sex with willingly, and thus it's up to adults to be responsible and avoid such encounters. Legally minors can't have a willing sex with an adult. So it's a rape and not alright even if both parties were fully willing, if nothing else then because the law says so. Somewhere else it might not be, but they were not somewhere else. Different cultures have different ideas on what is the appropriate age of consent, and the age is sort of "arbitrary" chosen, but it comes from the tradition and America is very puritan in pretty much everything else compared to Europe, so the same applies to this too. That's just the well established moral norm in the US society, so breaking it is obviously deeply anti-social and evil behavior, regardless of what age of consent is in my country or France or Brazil. Everyone involved was American, so even if you argue against the laws, still American moral and culture norms apply.