Full employment is a guarantee that if you want work, there will be a job. UBI is a guarantee that if you for some reason don't work society will still provide for your survival.

These can be done at the same time and strengthens anyone who needs to or can't work for a living today. They are only perceived as opposites because they both answer the burning question of how to provide much needed demand in our current and future economies. They also run into the same problem in moving power from bosses and owners and how to overcome that is the real question. But trying to win the Coke or Pepsi debate is easier I guess.