Someone said behind neck press is wrong,
But some people (including me) are doing it.
I tell you what nothing is right or wrong.
When people say something, you should think it first.
When someone told me you should not do behind neck press, or it will hurt you, perhaps his shoulders are already messed up.
If someone cannot do any behind neck press, I encourage him to do more shoulder #mobility drills and do strengthen his rotator cuff.
Similar to ass-to-grass #squat, someone said it's bad for your knees.
Look at the Olympiclifters. They must squat low enough to catch the barbell. Recently, I am practicing a lot of #Olifts; my knees are absolutely fine.
When someone can't do squat with full ROM, because he doesn't have the mobility to squat then tell others don't do it. And everyone have different body structure.
For example, some of my clients are not allowed to do Back Squat with powerlifting style, but they can perform Front Squat well. Depends. In Hong Kong, I seen a lot of people fail to sit-and-reach test. Their hamstrings and hips are extremely tight because of sitting at the office for too many hours.
So, when "someone" said something to you, you should do more research first. And I encourage you to find out why did someone say that. We need to understand the background and situation. It is also applied to #dieting. Every coach or bodybuilder has his own experience. We knew that "One size doesn't fit all."