Who gave Satan the authority?

The claim that Satan was allowed to drive the children of Adam (pbuh) into Hell could only have one of the following two implications..

The claim that Satan was allowed to drive the children of Adam (pbuh) into Hell could only have one of the following two implications: either what Satan has done was injustice committed by him against the offspring of Adam; or whatever he has done was just. In the first instance, if such actions were just, then Satan cannot not be blamed and there would be no reason for Christ (pbuh) to prevent him from doing what is right. Moreover, Satan should be granted the opportunity to take hold of both generations, those before as well as those after Jesus (pbuh). More seriously, in that case, there was no need for Jesus (pbuh) to come to the salvation of the children of Adam (pbuh). They simply do not need it.

On the other hand, if what Satan did was injustice and God did not prevent him from committing them before the coming of Christ (pbuh), we are faced with two possible scenarios: either God was incapable (God forbid) of preventing such an injustice; or He was able but did not. In either case then, there is no difference had injustice been prevented in one particular time or another, because God is either impotent to stop it or simple does not care. But this is not a tenable position at all, as the Blessed Creator is both Omnipotent and Ever Merciful to the best of his creations – mankind.