> I fear that our ability to use space to destroy ourselves will come before we can use it to launch a diaspora.

Will come? It is here. Have you not heard about intercontinental ballistic missiles?

In that case I have this bad news for you. Multiple actors around the globe maintain the capability to fling warheads at others (through space).

Not sure what you mean by “destroy ourselves”, but our capability of destruction is not constrained by cost/mass in orbit.