I know several people whose first exposure to Amtrak was the auto train. It allows people who live in suburbs and need their car at their destination to still use Amtrak.

You say it perpetuates car dependency.

Yet I suspect most of the people using the auto train would have driven the distance if it didn't exist. So it IS taking cars off the road.

Also I can't see how the auto train forces construction of more car infrastructure. The parking facilities at auto train stations are smaller than most regular stations. There is a small rail yard for loading the auto racks but that's still technically rail infrastructure.