Unethical to send people on a lonely, hazardous journey? That may be, but to send a solitary craft with a small number of explorers borders on simply bad planning. It is a plan which does not include redundancy. Sending a small flotilla, with multiple crews, capacity to transfer personnel between ships, and capacity for each ship to carry the whole expedition human crew, would provide redundancy in the event of a ship or ships becoming unserviceable. It would mitigate the boredom/loneliness problem, and increase the probability of the whole crew being able to return safely. Space is dangerous and things go wrong. The Apollo series demonstrated that. Early explorers learned to take several ships to increase their chances of survival.