I still can't buy the fact that rules and morals can be a catch-all. Can someone with that viewpoint explain in as much detail as possible why they think that's appropriate?
How complex of rules are you able to understand?
How complex of rules are you able to imagine?
How complex of rules have you been exposed to?
For instance have you thought about possible moral rules as complex as
"It is immoral to kill a non consenting individual that has not forfeit their negative right against murder or already in danger due to the amoral actions of nature or actions of others?"
(This is a extremely simple rule as far as applied ethical rules would go.)
However a simplified argument would be as follows:
P1) Ought implies can
1->2) There does not exist a situation without at least 1 moral option
P3) The universe is finite
3->4) There are a finite number of situations that can occur
2+4->5) There can exist a list/summary of the finite number of moral options in each of the finite number of situations
5->6) The rule mentioned in 5 can catch all.
Now there may be a simpler set of rules with equal validity to the rule mention in step 5 above.