If a bunch of hobbyists wanted to build a way to track cars using publicly available methods why shouldn't they have the right to do that? Could it be creepy? Yeah, but as long as they're not exposing information that's publicly available or targeting specific individuals, then it's not what I would consider to be morally wrong.*

*On the other hand, the government using public funds to do this, combining the data with private information, and trying to keep the fact that they do this secret is wrong in my book.