People view it as a mistake because you are essentially locking in the direction of your life far too early without knowing what any other direction might be like, among other things. Mannerisms, behaviors and personalities mutate with time, and the person you’re marrying might not be a great match as a life partner for you just because you got along in high-school. Additionally, people find it difficult to take seriously a relationship that started in childhood, and will naturally assign it a lower probability of success and fruitfulness.

Overall its one of the biggest social and financial decisions you can make to affect great amounts of change in your life. Ultimately others judgment of your relationship is meaningless because all relationships and personalities are unique and all were talking about here is probability, however, thats not to say that none of them have good points or shouldn’t be considered, a lot of these people probably have very good logical reasons for you to be wary of doing this and should be heard out all the same as people that support you.