>So I have to question the "no symptoms - zero transmission rate", because the latter is precise and the former is not.

You got some push-back about the precision of showing symptoms or not in other replies.
I think the real precision problem is what is known about the disease.

1. The consensus among experts who have studied this rare disease is that they *strongly believe* the transmissible stage starts when symptoms appear.
2. The disease is quite rare, even in Africa, so believing anybody has perfect knowledge of the disease... well, that is just not a reasonable belief.
3. We do know it is contagious.
4. No exposure = 0% chance of catching it.

If we believe the experts are likely correct, what are the odds they are wrong?
If they are wrong, what are the consequences?

A strict quarantine is (by the odds) probably not necessary.

What is the cost of a strict quarantine?
It would temporarily inconvenience a very small population for a few weeks.

A strict quarantine is 100% effective.
And it would inconvenience far less people in a year than we inconvenience every day for jury duty, traffic school, and TSA inspections.

It is not the odds of being right that are so important.
It is the consequences of being wrong.