Yes it is.  The reason for this is that the prosecutors do not have to protect the rights of the accused very much.  They have to refrain from violating the rights of the accused, but they do not have to positively help the accused exonerate him or herself.  In other words, if the defense lawyer is being really incompetent, for example, the prosecution has no duty to intervene to protect the defendant.  So long as the prosecution does not violate the rights of the defendant, it is trying its best to convict them, not to protect them.  This makes our system adversarial.