>Why is faster than light travel necessary? Plenty of space in our own solar system.
Between one unhabitable planet and another, plus some gas giants, etc., where's that plenty of space? Unless we also handwaving terraforming into the equation too (as we'll do with carrying any significant number of people via spaceships as opposed to small scientific missions, the 9+ months travel time, space radiation, lack of resources to eat/drink/breath there, etc).
Plenty of space in our own solar system
After all, what can you hide behind floating in space, fully illuminated by the sun?
Regarding technological development, again, on a long enough timeline, I don’t think it’s much of a concern. Technologies will continue to develop, quickly or slowly. It hasn’t even been a century since we walked on the moon. Deriving trends from this short period of time is not particularly relevant.