Final answer:
The negative mass Schwarzschild metric does not have an event horizon because escape velocity never reaches the speed of light, fundamentally altering the spacetime curvature compared to positive mass black holes.
This leads to a theoretical understanding that negative mass would repel other masses and not form an event horizon as in the classical black hole scenario.
Step-by-step explanation:
The concept of an event horizon is intimately connected to the idea of escape velocity, specifically when that escape velocity equals the speed of light.
In a Schwarzschild metric of a black hole with positive mass, the Schwarzschild radius (Rs) marks the distance at which the escape velocity is the speed of light. When dealing with negative mass, the nature of spacetime curvature changes significantly.
The lack of an event horizon in a negative mass Schwarzschild metric implies that at no radius does the spacetime curvature cause a 'zone of no return' where the escape velocity equals the speed of light.
This is a stark contrast to the positive mass Schwarzschild black holes where such an event horizon exists, indicating the possibility for theoretical reflection on the differences in spacetime geometry between positive and negative mass scenarios.
Another point to consider is the aberration in terms of physical law when talking about negative mass.
Such scenarios can diverge from our usual understanding of gravity and spacetime. In theory, a negative mass would repel other masses, and therefore, the spacetime would not warp in a way that would trap light or other particles; it extends the question into theoretical physics where standard interpretations may not readily apply.