Generally people aren't looking for immortality in the "evil magic curse" sense. They want immortality in the sense of being able to preserve your body and your mind in your prime indefinitely. A magic curse where you suffer forever is bad, but being healthy is good.
Life is suffering.
Completely disagree. Would rather be limbless and alive than dead. Constant pain? Constantly take opiates.
Then the opiates stop working so you take so much that you'd wish you were dead, because the pain doesn't go away no matter what.
Non-ending life (as you describe it) is terrifying.
But non-ending life (in other more positive conceptions) is the literal basis of religions.
Name a religion that doesn't actively oppress and break people and isn't also built on a long history of exploitation.