I think if GT5 is to embark in the online world; with its challenges, leaderboards and clans... Liveries and custom paint jobs are a necessity. The ability to customize one's avatar is not paramount to any online players and communities; it basically went from being en emerging gameplay to a full core gameplay mechanic.
Even most racing "clans" in the real world have war colors and custom designed logos for their cars.
Overall, some people are against it because they see it as something that is not necessary to driving, but then again its not to any kind of games.
Undoubtedly there are even more arguments for why visual customization is increasingly essential in Gran Turismo, but I have to get on with what's left of my day.
Many MANY years ago when I was just getting into racing and NASCAR/Winston Cup was the only thing available in "stock" car racing, I watched some single make races where all the cars were basic color schemes with no team liveries, and it just wasn't the same.
Part of the thrill of racing is to see some car with an incredible paint job making it's way through the pack. And that's why some of us buy posters of some racer or other, because his (or her) car has an eye catching livery.
I personally think most people's objections boil down to "I don't think I can make a nice livery, so I don't want anyone to be able to." I think the obscenity line is just not thinking things through or they're grasping for a convenient line. The world we live in is obscene. There's no getting away from it. Heck, Grand Theft Auto, piece of crap though it is, is a huge seller. But how many of you naysayers don't watch TV or movies because of nasty content? I think many are spouting out of both sides of their mouths on this.
As I said in another thread, the Forza community has grown substantially because of user created content, and there are some magnificent pieces of work from those either recreating some fantastic livery from the racing world, or as I do (did), coming up with our own.
And this is where I hope GT5 breaks ground. Racing online with plain street cars or race cars from the roster Kaz and the lads give us is okay, but it's much cooler than you can imagine to create your own racing identity with paint, racing bodykits and decals, and taking this car, unlike any other car in the world, on the track. In my opinion, This is why Forza is so cool. The racing isn't that much different. It's the ability to create something unique which is completely and totally your own that identifies you to a planet full of other racers. The worst thing I can imagine is a race full of the Raybrig NSX or the Castrol Supra.
For those of you who don't want this, can you imagine the worldwide outcry which would erupt if Kaz decided that only street legal sportscars would be in Gran Turismo 5? No race cars? And this is very much like what some of you are complaining about. "No. No modified cars." Does this sound like a good idea for a racing game? And how many of you who don't like modifications modify your cars anyway?
If you pick a race car out of the list, don't you choose one with a paint job you like? Wouldn't it be even better if you had one that no one else had? Furthermore, having racing bodykits and vinyls means you'll have a never ending car list. If GT5 is missing a car you wanted to see in the game, now you can recreate it. And if you can't, either Polyphony can give you templates to making your own, or some artist in the community can make one for you.
The only thing I can see as a negative is the crude art and language which might happen. But I have to say that in my experience online in Forza, I never EVER saw one. I know they exist, but their numbers are so few, you have a better chance of winning the lottery. And like I say, I doubt any of you lock your doors, refuse to watch TV or read any magazines because you might come across something offensive.
The only thing I can see for this subject is an even more enthusiastic reception for Gran Turismo.
Edit: skimming this thread, several of you echo my sentiments exactly. When a new race car comes into the racing world, give me the ability to recreate it. If I have an idea for a race car of my own, give me the tools to build it. That's going to have me playing Gran Turismo and no other game for the rest of my life.