Yes, there is a huge debate on here regarding that.
I am in the UK, and here it is the absolute norm for cats to go outside. In fact, when i adopted my latest cat from the shelter, i had to fill in a questionare, and sign a declaration, and i had to say that she would have access to a garden and i was willing to have a cat flap fitted. In general, we really do believe that a cat should be alowed to go outside. Also in the questionaire i had to say whether i lived on a main road or not, and if i had said yes, then i doubt very much they would have let me have her. Personally, if i lived on a main road then i wouldnt have a cat, because i strongly believe that they should be alowed to go outside.
Is it safer? Well, i dont know. We dont have the wildlife here that you have, so thats not a problem at all (as in racoons, bears, coyotes etc). People deliberatley harming them is not unheard of, but it is extremely rare. The UK is well known for being a nation of animal lovers. Then theres the biggie, being hit by a car. I will get thumbs down here, because I have lost 3 cats on the road, and the house that i lived in then was a residential area, and not on a main road. The 3 that were hit we actually took in as strays, and it was just not possible to keep them indoors. We actually believe its cruel to keep them indoors, we believe that cats should be alowed outdoors. i dont know about residential areas in the US as such, so i dont know if theres lots of main roads, maybe theres more traffic because its a bigger and more populated country, so cats have more chance of being hit by a car maybe?
The bottom line of it is really, theres two sides to this argument. The side that says its safer for them to be indoors, which in all honesty, it is. But then again, the argument can go that to keep them indoors is unnatural and is depriving them of living a natural life, and personally that is what I believe.
Maybe we should just not keep them at all?
Edit: However, i dont let them out at night. Most people who let their cats out would agree with me on this one. And I have also found that the ones who we didnt take in as strays, never really went out of the garden, and spent more time actually indoors than outdoors, but they always have daytime access to the outdoors via the cat flap.