Well laid-out, well-argued and, as an argument for religious tolerance, unimpeachable.

But still based on unsupported assumptions.

Common sense and logic agree that there was a First Cause -the Universe had to start somewhere. But the assumptions begin at that point:

Imprimis:

That the First Cause is intelligent and created the Universe intentionally and for a purpose.

Item:

That the development of intelligent life in the Universe is that purpose, or part of it.

Item:

That there exists a non-material portion of every intelligent being that survives the death of the material body.

Item:

That the purpose of that non-material part is to fulfil the conditions necessary for unification, or reunification, with the First Cause.

All of these remain essentially not proven. As such, it is important for people of good will to treat all religions as purely human constructs and to judge them on the effects they have, for good or ill, on individuals and society in this material life. Because some of them are damaging in different ways.

We should confine our concerns and energies to the things that lie within our power to understand and influence. We should also attempt, in all reasonable ways, to expand the range of what lies within our understanding and thus our power.