Alright, you guys have all given awesome answers (even if I don't necessarily agree with them), and I thank you all for that. I don't think anyone's gonna read this but here are my thoughts:
God did originally create man to be immortal. Because the world was originally perfect, there was no need to be able to escape it. However, when man sinned, his relationship with God was severed, and sin and death entered the world. Death actually was a mercy, so that we wouldn't have to live forever in a broken and evil world. But because we were made to live eternally in the presence of God, we still long for that (in a way).
When Christ conquered sin and death, He offered all who believe in Him an opportunity to spend eternity in the presence of God, which is what man was created for, as I said. But because we are in a state of rebellion against God, we don't want to have to submit to the One who demands that we give all that we have and are to serve Him.
And so we continue to seek to regain immortality by other means. Because we don't know what joy there is in following God, we want to be gods of our own, and not have to bend the knee to any other. But God, in His infinite wisdom and mercy, gave us mortality so we wouldn't get caught up in our sin and pride, but instead look to Him for eternal life.
But some still remain defiant. They don't want to have to be accountable to God. They want to be able to do whatever they want. And so they keep on looking, seeking for what isn't there, and being unable to find it, resort to wasting away their lives in temporal pleasures and comforts.
So those are my thoughts on the human quest for immortality. Is it inherently bad? No. Can it be misguided and lead down paths that are bad? All too easily. Can it lead us back to God? Yes, but only with the right promptings.
Again, this is my own opinion. I won't get angry if you disagree. But no matter what your opinion is on this, I wish you a great day!