Peter F Hamilton surmised in his Night's Dawn trilogy that antimatter would be outlawed, but produced by large accelerators parked close to suns in unoccupied solar systems. It was still heinously inefficient, but the high price of black-market AM justified the cost.

Putting speculation aside, we know that AM is fail-dangerous. For all current purposes, we have better alternatives. For long-endurance power sources we have fission. For weapons we have fusion.

I cannot personally think of a common use where the statistical certainty of failure outweighs the risk.