To me the thing about road riding is that it isn't as weather dependent. Roads dry faster than singletrack and barring a blizzard or downpour you can ride in most conditions -- tho as I get older i don't dig rain.
You can also go and see places you never would if you were driving.
I also agree that mtb has many advantages, but over the years I've probably spent more time on the road. One of the things that makes mtb fun for me is the change from the road, and traffic, but you can usually find some traffic free areas unless u live in a huge city. The hills of Morris county... the winding roads of somerset... good places.
That said, belligerant drivers aren't as big a thing as they used to be, it seems ... I used to run into some wierd ones,,. now the distracted driver is the issue. But over the years I've only had a few accidents, Worst one was a near head on by a left turning car driven by a woman with no US license... shoulder still hurts but she was clueless probably would have hit me in my car, too lol.
That said, more people riding makes it a more normal sight and therefore makes people more aware, our "car culture" ain't gonna change if u sit home. have blinky lights and wear a bright jersey. Dont be a bike ninja. Also take a pump and tube... flats are more common than offroad in my experience because of debris from cars.
btw if you get a cross bike with bigger tires you can do dirt road etc where there is little traffic. Ive even seen 2 crossbikes on singletrack at lewis morris