That only applies if you think that his actual argument is right. And as I've said before, Tony actually had the better argument imo. Marvel had to write him as a mustache-twirling fascist just to try and make Cap seem right. Cap's argument was, kind of stupid actually.
It's not all that clear cut. There's a lot more to unpack here than merely whose argument is right. Which is one of the reasons I'm actually more excited (with a pinch of nervousness... because the degree of difficulty is
high) about Civil War than anything else on the Marvel slate.
If the law were even handed and implemented in an above board manner, then yes, superhero regulation would be the way to go. However, the government (in the MCU) has been proven to be anything but rational, intelligent and even handed.
I'm speculating a little, but I think the government here will basically attempt to use a tragedy (likely Ulton) as a pretext to pass the SHRA, and use the SHRA itself as a pretext to essentially use superheroes as government sanctioned weapons. I can see why Stark would go along with the law itself... he'll be racked with guilt over the Ultron debacle, and thus might overlook the potential for the law's misuse.
So, while I see your argument about the correctness of the law in terms of its intent, I hope you can see my (and by proxy, Cap's

) argument about its possible (probable?) subversion in terms of its spirit.
What we do agree on, though, is that they need to make Stark's position come off as a lot more nuanced and a lot less fascist.