The problem is that the legal system has a quite noticeable element of randomness to it. Despite what you may have read, justice is not always done. (source: have been on the receiving end of this)

As a practical matter, if there is possible liability, everyone will have to have liability insurance, just as in the medical professions, for example.

You realize that reason could totally be "He's a police officer in 90210 and rich people don't like being pulled over for speeding".

Pretty sure cases like that would get thrown out. And even if some didn't, I'll that tradeoff instead of the current status-quo.