The idea of immortality is great, but not for everyone. We don't want every useless person to live forever.
Those who live forever should be great leaders, or scientists, or engineers, or great artists/musicians. These people could do wondrous things over the course of a thousand years. No need for Joe Shmoe at the gas station to be immortal though. He needs to make room for the next 20 billion people.
Religion is general against immortality for various reasons, but mainly because religion is obsessed with death. A true religious person works their whole life in order to improve their position in the afterlife. Many religious people want the apocalypse to occur so that God or allah can judge those deemed unworthy while the rest get to go to heaven. Immortality avoids this judgment that God is supposed to give you. Its stupid however, that's for sure.
They're also against cloning which is stupid. No idea why people are so butthurt about cloning. Wouldn't it be awesome to clone a human without a brain and extract their organs? Immortality is within reach at that point. Seems pretty win to me. All of the stupid ethics really get in the way though.
To be a great leader, or scientist, or engineer, or great artist/musician is not the only thing, that makes you useful for the society and for the human race. People, who are useful for the society and for the human race are those, who want to educate, to work, to create, improve things for the society, independently of the political situation, and the time period, that you look at. The useless are those, who don't educate. refuse to work, try to live on the back of the society, only want to get material help from the government for the entire their lives, without doing nothing in response. They are not only useless for the society, but are also dangerous for it, independent from the political situation and independent from the time period, that you look at. Nevertheless, a useful man or a useful woman for the society is some one, who has a high education for his/her time period, lets say an university education for our time period, wants to work, works in the moment, very often is doing a work, that needs advanced skills and advanced knowledge, thus this can be a scientist, engineer, artist or a musician, who is not great.
Don't the religious people have thought, at least one time in their life, that their religion can not be true? How about they prepare for the after life, then they die, and there is no afterlife after all? Will they be still this keen for the death?
I am also for the cloning. The perfection of the cloning will allow the human to multiply on the both ways - sexual and asexual, and thus to get a very strong advantage, compared with the other biological species, plus this will give the human race a new way of preventing the death of the human race.