You didn't explain how it makes a car safer.
Aesthetics and heat are irrelevant because tinting is illegal. I imagine tints are available that do not block visible spectrum but do block infrared and/or UV. If heat were the issue these would be satisfactory.
Tinting is not entirely illegal. It depends on what shade of tint you purchase.
There is a certain shade that you can have on your front windows and still be within the law. You can tint your rear windows any shade you like. It's only the front windows that you can get cited for if your shade is too dark.
If you've ever been in a vehicle with tint, you will immediately feel that it adds a level of security. It's more of a feeling of security. Tint also helps deter potential burglars, as they are less likely to see within your vehicle.
For example, during Christmas time, many vehicles get broken into in mall parking lots because gifts are there in the open for everyone to see. Whereas, if you had tinted windows, the chances someone could see into your vehicle is less likely.
There are many workers out there with all types of work vans, such as Astro vans and what not, that have tinted windows so that no one can see inside. This keeps their equipment safe from potential theft.
I think you catch my drift. In the end, tint is a personal preference, but it's not entirely illegal, as I mentioned.