Here's what I think.
There is separation of Church and State. An elected official shouldn't be elected because of religion, and in matters of state 'God' shouldn't be there.
Especially considering, for instance, "Under God" was added to the national anthem after it was written, as was "In God We Trust" to the money.
Not sure if "...or so help me god" was added, but if it was then it probably should be removed. This is a secular state for a reason.
Religion has always, always ALWAYS fucked up a country.
That said, getting yourself in a tizzy over a simple utterance is retarded. Just change "So help me God" to "So help me Allah" for a Muslim, or "So help me Yaweh," and if its an atheist, how about "So help my people?"
In fact, why not "So help my people" for everyone? Then it doesn't MATTER.