I don't see the logic in that final statement either.

Go back one step to your previous paragraph-

"For all force in the universe there is an equal and opposite force acting and thus the sum of all force is zero."

Two forces, equal and opposite, does not mean there aren't still two forces.  It is only when those two forces occupy the same space and time that they become zero, or nothing, all the time they are apart they are real and something.

The same with two particles which when separate are just that, two particles, but when combined annihilate each other at which stage they are nothing.