Just because it's your supported constitutional right to say it doesn't mean you can expect no social repercussions though.
This.
Besides which, it's just generally impractical. The preparedness should match the risk, erring a bit to the side of over-prepared. Well, generally speaking, a handgun meets this requirement, and is not an attention-garnering encumberance.
As was also touched on, the rifle is more an offensive weapon with it's range. It follows that one would only carry it if they are expecting (or even looking for) trouble.
Now, keeping a long gun in the car? Different story. The car doesn't mind the extra weight and it's not going to be seen (usually). I keep an AR in the trunk. I figure if there's ever a situation where I need that kind of firepower in addition to my CCW, I'll most likely have ample warning and be able to get to the vehicle and retrieve it.
I would view the OC of rifles a bit differently if there was a hightened risk in a given area on account of a credible threat. For instance, we find out that some terrorist group is planning to coordinate bombings and shootings on a large scale all over the country; Yeah, I'd probably up-arm from handgun to AR-10. I'd also be at an entirely different level of situational awareness. Barring a situation like that, though, I just don't believe it is practical and prudent.
heck, its even odd to see police with long arms.
Even more to the point. When you see officers toting long guns, you wonder what's going on, because it
isn't normal. Usually they're only so-armed in a heightened risk situation.