Really, now.

If this were such a bad idea, and the theives such brain trusts as to readily disable the systems, then how is it that they're *failing* to disable the OnStar system already? Many hundreds of vehicles are recovered each month via the offices of OnStar right now, so we can pretty safely conclude that there are a very large number of idiot theives out there who have no bloodly clue about OnStar, nor how it might work against them. Once they've been hit with a slowdown command, it's a bit late to start learning.

It's not going to cost extra money, so there's no argument against that, there, either.

Hacking the signal to monkey with traffic? Yeah, I suppose that's possible. Remotely. But I'm not going to lose any sleep over that possibility. The people with the skills to do that generally have far better things to do with their time, things that actually earn them money (legitimately or otherwise).