If we are talking about pure logic: it boils down to the probability of just a sucessful return vs the probability of when that return will be
A return trip to Mars will be successful IF:
The return craft is not damaged,
All members of the crew remain healthy enough to prepare the return craft,
supplies do not run out.
If the return craft fails, or the crew are unable work to prepare the return craft before the supplies run out, the entire crew will die. Space travel has too many unknowns to realistically give a chance of survival of a return trip.
By taking out the return, we have to assume and plan that there is no minimum survival date. Then we get this scenario:
Robotic construction equipment and materials are sent to Mars. Controlled from earth; solar power, water cycle equipment, machines to actually convert CO2 into breathable oxygen, and comfortable habitation are all constructed. These are sent as many, smaller missions so if one fails it is not the end of the effort.
Many "one way craft" carrying food and spare parts are sent to the red planet over a long period of time. Each supply mission increases the reliability of the craft.
A Large team of space colonists are sent on a one way trip using these now tried and tested vehicles. They arrive at Mars to a fully functioning, powered, habitable colony they can occupy indefinitely on food supplies sent from earth. (This would consist of many small supply missions carrying a surplus on the assumption some will not make it)
The large team is then sent ample supplies of food, materials and equipment to expand and maintain the colony. As the colony expands more are sent - the colony is subdivided into small independent units so if one fails the entire Mars population is not killed.
Eventually the colony becomes populous enough that return vehicles are constructed and two way transport is possible. The original colonists, all be it 10-15 years later, return to earth to a heroes welcome.
I have quite a nice life on earth with a nice family. Of course I would like to be a Martian pioneer, but would want to be given a decent shot of returning to earth. If going on pure logic - this way I can say there is a very good probability I will be returning to earth alive – even if I cant say the exact date.