The fact is that any manned vehicle capable of interplanetary travel is by the nature of the energies involved, also a weapon of mass destruction. A spaceship is a weapon in the same way a car can be a weapon.
So either you massively restrict access to this technology, or you create a system of surveillance and defense that is so pervasive and effective that it makes 1984 look benign, OR you just say fuck everyone else and use that weapon to remove yourself from range of everybody else’s weapons.
Proliferation is an existential problem for anyone in range.
Akshually, there’s only one Sol-ar system.