Human missions to Mars are appearing feasible and choices must be made on whether to support them. However, debates on this matter are increasingly polarized. To support constructive discussions and sound decision-making, an interdisciplinary European group of over sixty world-renowned scientists, astronauts and science fiction writers conducted a thorough analysis of the most popular scenarios dealing with a human presence on Mars. The outcome evidences a wide variation in the feasibility of these scenarios. It also underscores the immense value which could be produced by sensible human missions to Mars, as well as the tremendous risks they would pose if performed without adequate consideration. For instance, small-scale exploration missions could be implemented in the coming decades, while terraforming is largely beyond any technology that we can envision. Science-driven missions are worthy but picturing Mars as a fallback plan, should the Earth be devastated, is misleading and unethical. Catastrophic breaches of ethics must be avoided without forfeiting the exploration of Mars. This requires gaining an ability to discuss the matter with nuances, relying on established scientific knowledge, considering scenarios one by one rather than as a whole, and refusing to let the exploration of Mars become a partisan issue.