I understand that. I just don't understand is why it bothers you so much.
If people just passively accepted that that the intent was to make the USA a Christian nation, and that believ never spilled over into politics and lawmaking, it would still be as worth debating as, for example, incorrect understandings of other historical records, scientific principles, etc.
However, the incorrect understanding is also used a justification for passing laws that many people, some of whom are atheists, feel should not be passed in a secular nation.