Let me make this exceedingly clear for you: do not resort to insulting others simply for not sharing your opinion.
News flash: people like different things. Luckily, you are not the arbiter of what a "real driving or racing simulator" is and isn't about.
For you. Polyphony obviously sees things differently — you know, since they're including a livery editor — so this "it's not proper" crusade is doubly silly. They've already encouraged visual customization in the PS3 games anyway: I could quite easily load up GT6 and paint a car bright neon pink with contrasting baby-puke green wheels, if I felt so inclined.
Allowing players to design liveries also frees up PD from pesky things like licensing and the time needed to do them themselves. If the livery editor is powerful enough, we can see absolutely every real-world racing team's R8 LMS recreated, plus any sort of small variations players can think of.
Yes, let's actually think about it: why do other games with functioning livery editors not all carry 18+ ratings? For the same reason they all carry fine print about how the online experience can't be given an age rating.
A simple report feature, like the one in place in games like Forza, LittleBigPlanet, or even GT6 (for custom tracks), where players can report offensive material, would solve most issues. Case in point: I've seen precisely one offensive livery in the 10 months I've played FM6 online.
Besides, a simple "Do not show custom liveries" checkbox in the options menu in GT Sport could solve this issue for those that find other peoples' creativity to simply be too much.