The reality is that, when it fails on jenkins, you'll have to reproduce it locally to diagnose anyway. The scripts are designed so that you can run them locally without problems. It'd be trivial to write a script to download a build's workspace and re-run the script to see what happened. I agree we might need the switch to diagnose problems with the jenkins setup, but we can always turn it on when necessary.
In the mean time, i'd say shorter logs are better because you can better spot problems that the script misses erroneously.