I have a different opinion on this...
Installing an HID to a car that does not have a lens, makes the light scatter thus in most cases blinding the on-coming driver. This too can be reduced to a certain extent by adjusting the reflector and proper focusing.
Then there are cars that came from factory with the lens, but without HID... and these, even with the aftermarket HID don't scatter light.
Example, my 91' E34 has the lens on the low beam and I installed a Philips HID. My friends 99' E46 didn't come with a lens on the low beam.