> the bike seat cuts off circulation in point where a lot of blood vessels pass through, riding has been linked to cancer

Even if this is true (I'm skeptical without seeing a source), you're more than free to mount whatever style of seat you want on your bike. No one's stopping you.

> Along with the more common city riding hazards like car passangers opening doors, falling over and you breaking bones, getting run over, or even directly breathing in exhaust fumes from trucks.

Great point. Those are all excellent reasons for further reducing the numbers of cars on our streets in lieu of bikes and walking.