Law & Order doesn't understand the Fifth Amendment?

Picture this: any of the male protagonists, doesn't matter if it's Goren, Stabler, or that guy from the original L&O is attempting to coerce a witness or suspect. The witness or suspect doesn't want to talk to him. male protagonist calls it obstructing. The witness/suspect is intimidated. Normal person calls this not wanting to testify against oneself. Somehow what the detective is doing is constitutional.