I love riding outside. There's nothing quite like it. The trees, the mountains, the quiet... I'm really fortunate that I live somewhere that has countless miles of quiet roads, no traffic lights, and tons of dirt (gravel, if you like) roads where I rarely see cars, and almost never ever see another cyclist. When we lived in Colorado I loved riding outside, but there were too many close calls, too much yelling out the window, too many horns honking, and not enough rides when one or more of those didn't occur.
Indoor riding is safe from a "no cars" standpoint, but I tend to ride a lot harder on the kickr. And I *LOVE* it! Probably because of the power meter, and the ability to kill it for a while and if I get bombed out I'm already home.
Ride inside, if that's what you like. I do.