The point here is that if such a tick box or button were provided together with a warning, then a cusomer would not complain because... well a warning is a warning. Simple.
Except that it's not that simple, or we would have done just that.

Think over the consequences a little. Let's say that a user turns the option off while trying to rectify some graphics problems. Maybe it appears to help. Maybe it really does help. A month later, the game starts crashing for no obvious reason. Who will the user blame for the crashes?
Or another example. Content Creator Charlie makes really awesome scenery splines - fences, hedges, that kind of thing. They look far better than the built-in content, but they cause the draw distance to reduce a little. No problem! Just let everyone know to turn off the little switch in the settings. Your machines are powerful, they can handle it. Everyone starts using Charlie's content in their routes, because it's far better than the available alternatives. All the creators in the know, all the best routes use his splines. Now anyone who wants to use those routes is seeing draw distance problems. No worries! Just turn off that little switch. Except the game starts crashing on some machines. Still no problem, you say. Turn the switch back on! Except now we have a lot of users who are locked out of all of the good content forevermore. There's no reason they should be locked out- if the splines were built efficiently in the first place none of this would be happening, and frame rates would be better as well.
Your argument is "if you allow us the option now, some of us might be able to avoid problems running route X today."
My argument is "if we prevent the option now, everybody will be able to run all the routes in the future."
In both cases somebody loses out. In your scenario, some people win out in the short term and everyone loses in the long term. In my scenario, some people lose out in the short term and everyone wins in the long term. We're not in this for the short term.
Hope this helps you understand our decision,
chris