You are being asked to lower your headlight adjustment because HID lights were never designed for use in halogen reflectors. You are blinding the crap out of oncoming drivers with these conversion kits.
When a bulb is mounted inside of a parabolic reflector the light emitting portion of the bulb must be precisely positioned so the reflected light in is properly focused and beam shape is tight. HID bulbs are longer than halogen bulbs so the HID emitter (the little bubble containing the gas) is pushed further out into the reflector, therefore it is out of focus and scatters light all over the place. Even if you angle your lights down some you are still blinding oncoming traffic and wasting the higher output the HIDs provide by scattering the light all over the place.
Also, don't go too crazy with the higher kelvin temps. After about 6000K the output begins dropping off. As well, the blue color end of the light spectrum is the hardest for the human eye to focus.
If you want HIDs, then spend the time and money to do it right.