You want to know why the Ten Commandments is bad in a courthouse? Because it would give weight to decisions made for reasons like this:

Death penalty tossed over bible verses
The Colorado Supreme Court on Monday threw out the death penalty in a rape-and-murder case because jurors had studied Bible verses such as "eye for eye, tooth for tooth" during deliberations.
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The Supreme Court said that "at least one juror in this case could have been influenced by these authoritative passages to vote for the death penalty when he or she may otherwise have voted for a life sentence."
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[T]he jurors had gone outside the law. "They went to the Bible to find out God's position on capital punishment," she said. Prosecutors had argued that jurors should be allowed to refer to the Bible or other religious texts during deliberations.

You know the part that scares me. I mean, other than the fact that Colorado, while red, isn't one of the MOST conservative places and if that's what they do there, what exactly are they doing in Texas, Alabama, Mississippi, etc? They just ignore the entire New Testament. Where Jesus talked about turning the other cheek. Where he spoke AGAINST most of the commandments in the Old Testament. I mean, if you are going to be all religious, at least don't rely on what your guy argued against. (Except if they were Jewish, in which case I am ok with that).