Amazingly, the question asked for centuries, and asked scientifically for over a century, still has no answer: Does Mars have life? Even the possibility of surface or near-surface life at Mars has not been scientifically answered. Conversely, the surface of Mars has not been proven sterile. So should we return samples of Mars to Earth without even knowing if the samples contain microbes or other life?
There are at least six significant but controversial signs that Mars has surface or near-surface life. (See Overview of Mars page via the menu at the upper right). However, to scientifically declare Mars has life, definitive proof would be required. I’m interested to collect the opinions of people, especially amateur astronomers, to the question: Does Mars have life? Also, does that opinion affect your concern of the danger of a Mars pathogen or invasive species being returned to Earth in the upcoming Mars Sample Return program?