If your society has spaceships and starships and antimatter fueled warp drives, it is probable that it has slower than light ships that can reach relativistic speeds, and faster than light ships that travel at multiples of the speed of light.
Space ships that can travel that fast make terrifying kinetic weapons, regardless of their power sources. The impact of such a ship with another objects is likely to cause an explosion similar to or greater than the explosion of its fuel supply without a collision would be.
So the deadly danger would be the spaceships as well as any antimatter fuel they contain.
Therefore, spaceship trajectories would be highly regulated anywhere near a solar system with inhabited planets. Spaceships that approach the solar systems with threatening orbits, or spaceships within the solar system that suddenly deviate from their approved orbits, would be attacked, vaporized, and/or diverted first and questions asked later - if there are any survivors or intact flight recorders.
In the Star Trek: The Next Generation episode "Haven" (30 November 1987) an unidentified spaceship is approaching the star system of the planet Haven. Valeda Innis, the First Electorine of Haven, calls the starship Enterprise which happens to be in the Haven system:
VALEDA [on viewscreen]: An incoming vessel has bypassed our stargate, violating our law. It has refused any attempt at communication.
PICARD: Are you saying you believe it to be hostile?
VALEDA [on viewscreen]: Failure to communicate is inherently hostile. We have no defensive capabilities here and our treaty with the Federation specifies your obligations in that matter.
The stargate is not described and it is uncertain what percentage of other star systems have stargates.
It is possible that the stargate is the exit point of a some sort of space warp leading to another solar system. The voyage through that space warp bypassing many light years of space could be much shorter and faster than travelling though those light years of space, even with warp drive.
Because of the many, many, many problems and inconsistencies with speed, distance, and time in every Star Trek production starting with TOS, there is
a theory that many interstellar voyages in Star Trek involve travelling through one or more of those hypothetical space warps to vastly shorten the journey length and travel time.
So the idea that the stargate in "Haven" could be the exit of some type of space warp used for interstellar travel is very attractive.
Another possible theory is that the stargate in "Haven" is some type of vast space fortress that all spaceships that approach the system have to match velocity with and dock with. The spaceships are inspected for contraband and alien germs and the passengers and crews checked. Then the crews would probably be sent to the destination planet as guests/prisoners in a separate spaceship manned by a Haven crew and another Haven crew would board the ship to take it to Haven.
All Haven citizens allowed to operate spaceships in the Haven system would be psychologically profiled and selected for extreme loyalty to Haven, and their families would be held as hostages. Whenever a spaceship deviated from its assigned course the families would be tortured and images of the torture broadcast to the spaceship until it returned to the assigned course.
Presumably a Federation starship would be exempt from the requirement to stop at the stargate.
Antimatter would also be very strictly controlled. Antimatter would be produced in gigantic space factories far from anything that could be damaged by a gigantic, planet-devastating, explosion. The antimatter that was sold to customers for spaceship or other use would be in containers and legally considered to be "Sealed Evil in A Can".
Because misusing a tiny amount of antimatter is equal to releasing Cthulhu upon an unsuspecting world.
Presumably the containers, and the spaceships and installations that used antimatter, would have complex AI programs to determine whether the antimatter is being used properly and whenever the programs suspected intent to misuse the antimatter they would unleash killer robots to kill first and ask questions later.
Thus the spaceship-using or antimatter-using characters in your story would be constantly worrying and checking that anything that they did with spaceships or antimatter was not only legal but also didn't appear to be even the least bit suspicious, since they would live in constant fear of the horrifying penalties for doing anything that seemed even the least bit suspicious with their spaceships and/or antimatter.