The drinking laws occurred mostly because there were exponentially increasing trends of car accidents and loss of life due to sizeable drinking irresponsibilities. It makes sense laws were prioritized. 

Also, a sixteen year old can be potentially mature enough emotionally and mentally to handle a relationship with an older partner. Thus why I do not consider it immoral for those pursuing relationships with them. But I do not demonize other people's attraction, interests, and so forth based on such a innocuous thing. But yes, feel free to question it if it is not in line with your morals or ethics -- like I said, morality is subjective.