Alright. Let's look at street courses. Last year we had a terrible crash at Baltimore. It injured several people and ended the career of 1 driver. One of the biggest issues with where the crash happened and location of the grandstand. The grandstand what located very close on the outside of a fast corner. It was begging for debris to go flying into the stands.
Now let's consider the corner design at these street circuits. For an f1 street circuit, most high speed corners have extra tire barriers or an escape road for a car to abort the corner or soften the blow of an accident. For Indy they have the walls located very closely with limited crash absorbency.
F1 is very particular about where they will race for many reasons. Money is a huge, huge factor, but they also have to ensure that it is an FIA grade-A circuit. Grade-a circuits have to meet rigorous safety standards in terms of design and safety for drivers, track workers, and spectators.
If Indy was more selective on what they require from their circuits, they could put on a safer show.
Ovals are also a different matter. There is only so much safety they can provide at an oval, but I will discuss that another time.
Here is a great comparison:
Monaco:
http://m.youtube.com/watch?v=HjlUrckR8EI
Baltimore:
http://m.youtube.com/watch?v=A0Ny6F9PMOg