I have been thinking a little more about the two witnesses being required in death penalty cases.
In the context of the JWs being an religion based on archaic laws, that rule makes sense in their religious framework. They view disfellowshipping as a spiritual death and, as a literal death as well - ie...you will die forever instead of live forever if you are not a JW. They condemn the sinner to death.
What the retention of the two witness rule does is expose the cruel ideology of the JWs: if you don't behave, we have the power to 'kill' you.
Disfellowshipping is a death sentence. That is how harsh the judicial system of the WT is.
*to add...with all that said, the two witness rule is all about whether or not the offender/sinner will be disfellowshipped. It has nothing to do with establishing guilt - it has to do with the harshness of the punishment. If you put the scripture in context, it goes on to say that matters other than those that require the death penalty, are simply taken to the priests to decide