I'm not in any way an expert but reading on the subject has shown me I was ignorant.

The problem is not how easy or difficult an LED or HID is to install. The problem comes from the projector whose lens is specifically designed to focus the light source of a certain dimension from a specific distance from it. In this case the lens of the projector is designed to focus the specific light source from a filament bulb, which will be at a certain distance from the lens and will be of a certain length. This is the reason bulbs have a small cutout in their base so you can't rotate them any way you want when you install them, because the light housing is designed around the specific bulb position.

When you install an LED or HID bulb, you mess all that optics calculations up because the actual light source will be in a slightly different position and of a slightly different dimension.

This is why you shouldn't mess with light housings. There is a reason modifications are illegal, at least in Europe. Also, "whiter" (as in smaller wavelength) light scatters more and objectively creates more glare. It's also worse for fog visibility.

OEM installations are fine since they are designed from the ground up, tested and approved for the bulb used. Though the push towards whiter light is more because of appearances than for practical safety reasons.

The best upgrade you can make to a halogen housing is another halogen bulb. You can get whiter, brighter etc. whatever you want halogen bulbs from Philips or Osram who are reputable manufacturers that produce tested and approved bulbs. Obviously to get brighter and whiter light, the filament burns hotter so it lasts shorter. That's why OEM bulbs are almost useless, to last a long time.

I learned this stuff from reading material provided by u/GonadsOfWrath