Rather than argue, as I am wont to do, I'll just concur.
But it's not just a post-theistic problem. The concepts of good, evil, justice, and morality aren't just monotheistic fragments. They're part of an overall social mythology. You can explain those terms with a genealogy ("good" really means "good for me," "justice" means "fairness," etc.), which reveals that the problem is really the use of the words, which is as arguments unto themselves, like "murder is evil." Though you can break that sentence into a definition that makes a lot of sense, it is unfortunate that the people saying it wouldn't be able to do that.
What would be better?
I think policy reasoning in legal theory is a good way to sidestep those sketchy terms. Maybe we should replace mens rea with whatever is Latin for "you should have known you were gonna get prosecuted for this."
As for lawmakers making allusions to scripture, some examples:
"Just like David facing Goliath, we must stay the course in the Middle East against all odds."
"Just like Sisyphus' insurmountable task, we must stay the course in the Middle East against all odds."
"Just like the old man reeling in that giant marlin, we must stay the course in the Middle East against all odds."
Why would a politician go with the first one? Besides the fact that it's the most positive analogy, followed by #3 and #2, respectively, the Old Testament is simply better known than Greek mythology or Hemingway. If the intent of the speech is to make an easy analogy, the Bible is a legit way to get it done. But when you're suspicious that it's mostly to inspire Christian rightiousness in the public, you're definitely right.