It's invasive because it's not medically necessary. The potential privacy and rights implications of the questions are obvious, particularly with the government getting in bed with the medical establishment with Obamacare. I can agree with you in the respect that, on its face, its relatively innocuous.... the thing is, I'd feel differently about it if it wasn't readily apparent to me that the government is just ITCHING to compromise doctor-patient privilege at every opportunity they can get. With these loon toons shooting up schools or whatever, government figures are trying to come up with ways they can get the public to suck for more invasion into their personal lives and medical histories.
This situation kind of reminds me with the same kind of disconnect people have with LEOs these days. For example not all that long ago when a LEO was pissed off at you it was because you possibly or probably did something that was actually bad. Now because everything is illegal and there is a machine above the LEO pushing for arrests and prosecutions of stupid malum prohibitum crap, the "machine" has effectively invaded the space that used to be only occupied by the LEO, the citizen, and the town's interests maybe.
This thing with the Doctors is no different- the .gov is readily invading that space between the doctor and their patients.
That said on the ground with this issue at moment I've never had my doctor ask this question and it's never been an issue for me, so it's not something that I'm always thinking about, either. I think in most cases right now its an issue easily dodged and its not worth making a mountain out of a molehill.
-Mike