I think that's too broad a brush, honestly. I would venture to say everyone on this board has some "fallback" phrase or reaction they immediately resort to when they're frustrated.
It might not be a curse word per se, but it could be anything from "darn" to "ugh" to a simple close-mouthed groan. A youth pastor I once encountered blurted out "Mickey Mouse!" whenever he was frustrated. :lol:
These examples might not be offensive to some in the same way cursing is, but they serve essentially the same purpose — and display no more intelligence than employing a curse word would. Human beings in general don't tap a font of immense creativity when it comes to voicing immediate frustration.
Unless someone is in the habit of bursting into Shakespearean haiku when they get mad, I think it's a bit of a canard to use the old saw of "people who curse display less intelligence than people who don't."
But damn it, that's just my opinion.