No planet is more earth-like than Earth itself, so if life really does pop up readily in earth-like conditions, then surely it should have arisen many times right here on our home planet? And how do we know it didn't? The truth is, nobody has looked.
“Missionary zeal does not grow out of intellectual beliefs, nor out of theological arguments, but out of love. If I do not love a person I am not moved to help him by proofs that he is in need; if I do love him, I wait for no proof of a special need to urge me to help him.”