It mostly depends where you are in America, but generally speaking, "Oriental" is an offensive term, especially when used as a noun.
It's basically the equivalent of calling an African American a "colored."
In some parts of the country, both of those terms are acceptable to a certain extant ("Oriental" is still sometimes passable in the Northeast, while "colored" is apparently still in light use in the South).
It's offensive because of the time it came from and how inaccurate it is.
That's kind of a funny statement and may exemplify why you're so confused about its connotations.
In reality, "The Orient" was considered Asia as a whole, so it makes no sense to define East Asians specifically as "Oriental". Moreover, it's sourced from a time of European Imperialism, when Europeans were trouncing Asia and taking advantage of Asians (meaning Indians, Pacific Islanders, Chinese, etc.) in general because of their inferior military technology.
Regardless of the reasons, it isn't that hard to use the word "Asian" instead.
I've never understood why some people are incapable of simply maintaining a level of politeness towards others. If someone doesn't want to be called something, I see no harm in abstaining from calling him or her that. It's irrational to go out of one's way to use terms that are offensive to that person, regardless of whether or not one is ignorant of why the term is offensive.
Also, Persians have been asking to be called Persian as opposed to Iranian for decades. It isn't a new thing. They'd rather be identified with the nation it once was, not the nation it currently is, and I can certainly understand that.
