It is not as easy as you suggest. What do you say when a student says, "then why did no one recognize these human rights for all those many years throughout the history of the world? And why do many countries even today not recognize them (and to this 2nd question you cannot point out that people that do not believe in God as their supreme being, have someone else that they look to as being "supreme" and thus ruling over them.
For, you see,if we cannot explain that the right is given (granted) by God, and we say it just "is" then the students cannot quite fathom how something just is, with no authority behind it. For instance, I can say, "I own this house, I am a homeowner." But in reality without a proper deed to show as evidence and authority, how would I be believed if questioned? I cannot just say, "I was just born with it, inherited it." Rather I need some entity with proper authority to back me up. Thus we cannot leave God out of the equation when we claim inalienable rights.
America was founded upon the concept of the God of the Bible, and atheist can deny that all they want, but it does not change the facts. The government the founders set up allows people to chose to worship other than our God, or even to not worship any god. But they did not foresee a future where the God-less would actually be able to take over the country.
Indeed, without recognizing the ONE ultimate authority,
all this discussion of right and wrong and where rights come from,
is simply a matter of opinion, enforced by the ability to use force.
You cannot legislate in the name of God. We unfortunately do live in a world without recognition of God’s sovereignty. No one will accept “inalienable because of God” without then questioning all the evil and asking why God allows that to happen.
Unfortunately, in a fallen world, we do turn to authority to _guarantee_ our inherent rights. Perhaps the correct question is how did ‘guarantee’ become ‘grant’? We’ve come a long way from the Magna Carta, yet that was a case of people demanding that monarchs, who had the authority of God at that time, recognize the rights inherent to all humanity.