The plans that I've seen discussed are not, strictly, "one way". They're more akin to "go, once we have methods to regularly supply you, and we'll develop the infrastructure needed to bring you back at some point in the future".
That's not , perhaps, any worse morally/psychologically than the original Tudor shipping to the States. Thousands went there with little belief that they'd ever return.
...And a part of me wonders whether dying of old age on Earth is any better than the same thing happening on Mars?
Andy