If it is only to explore and understand Mars, then it is likely that we needn't ever set foot there to accomplish those goals. However, if the reason is 'to be there', or 'to spread our species across multiple planets', then I can see it happening. Perhaps more likely, the reason will be 'to get there before X country does'.

At any rate, I don't believe that a one-way trip is immoral if it is to accomplish the first two of those objectives. Unfortunately, the third objective is the one that would be more likely to make it happen.

Yeah, too true. I just still see that leading to an all-too-familiar scenario in which we visit a heavenly body without the intention of establishing any permanent and sustainable presence. We'd plant our star-spangled banner, and then die, at best maybe one or two generations later. There's no incentive for any one country to fund a colonization effort.

The only way I can envision a lasting Mars base is if every first world country decides to scrape together a program primarily intended to guarantee the survival of our species. Obviously that's not happening anytime soon.