It depends where you live & local culture, OP. We had kids playing footie, cricket & tennis regularly down the length of our road only 10 years ago. I liked it. That was an immigrant neighbourhood, though. Most of the young sportsmen lived on nearly very busy roads, overcrowded houses with small gardens, they didn't have other play spaces within 3 min. walk.
Bottom line is society standards have changed from you were young and most adults don't expect kids to be out in roads or on bikes except in little cul-de-sac type places, quite close to own home. So beyond that small space close to own homes, there will usually be problems & little tolerance.
I live on a quiet country lane & DC play out in the road when we we can supervise & watch for cars.
That "more cars on the road" argument makes me laugh. I grew up in 1970s California & we had vastly more vehicles to deal with than anything DC will ever encounter as children. We played out on roads & everywhere else, too. It's perceptions about acceptable risk and shared public space that have changed the most, not road conditions.
Your argument is a little one sided. There are fewer and fewer playing spaces for children these days and although some roads are dangerous, I know there are also some considerate enough to slow down when they drive down a road where there are likely to be children. I do agree that my Children won't be playing near any Chelsea tractors on the Kings Road!
I know this sounds like a joke but I'm trying to make a serious point - as a kid, my friends and I always played in the road, is it still socially acceptable or is it more dangerous?
In the mid eighties my friends and I would always be playing on our bikes, skateboards and make shift go karts in the road. When a car came, we'd all shout "CAR!" and move to the green (the grassy bit in the middle) or onto the path. I actually believe this made us all hyper aware of cars and their presence and may have saved me several times on nights out in my early twenties!
Now as a parent, I live in a similarly busy road but there are so older 'kids' with cars and mopeds and I feel it's too dangerous! Am I worrying unnecessarily? Do you let your kids play in the road?