The Ten Commandments are "lessons from the Torah," so Geary's exhortation to hang them alongside lessons from the Torah is redundant. But it does bring up some core issues, namely how shared texts would be claimed, how religious texts of any origin would be selected, translated and/or abridged, and how they would be explained.
When a teacher is asked why Roman numerals appear next to the words of the Ten Commandments, will she know that the Roman Empire criminalized Torah study on penalty of death, which makes the placement of Roman numerals with any Jewish text about as respectful as using Nazi swastikas? Will she know that Hebrew letters also function as numerals, so their placement next to the Commandments would at least be more culturally appropriate?
More to the point, why should she be required to know any of these things? It's not her job to teach the nuances of religious history or to enforce boundaries between the study and the practice of religion (boundaries that are, for many religious people, somewhat less than relevant). Such instruction belongs in religious schools, not public schools, unless religion is the subject specifically being studied.
Geary declares that Americans don't have the right to impose their religious tenets on everyone else's kids, but the display of sacred texts in public-school classrooms, whether the intent is to impart moral decency or to enhance the "study" of religion, does just that. It imposes someone's religious views--or, more accurately, what someone has decided is the least common denominator of a particular religious view--directly into the line of sight of schoolchildren, some of whom might belong to a different religion or to no religion at all.