Trademarks and Keyword Advertising

I think companies who have a long-standing trademark have some type of case that others who adopt it in a domain name, in a way that can cause confusion, infringe on their IP. A lot depends on the details, but there's at least some prima-facie reason for a claim.

On the other hand, there's another objection that I don't buy: some companies claim that competitors' ads that show up on key-word searches are infringing on their trademark. For example: let's say I search for "Lexus" and Google displays ads for Mercedes and Hummer dealerships. How is that an infringement on Lexus's trademark?

Suppose one sees a Fidelity advertisement, that convinces one to save for retirement and makes one think they're a good firm. So, one goes to a financial adviser and asks to open an account with Fidelity, and he suggests going with Vanguard instead. How is that a violation of a trademark?

Yet, the legislators in Utah have decided that Internet users who search for a trademarked word should not be shown ads by their search engine. Here's the law. Read a critique of the law here, and a defense from the legislative sponsor here. (HT: Slashdot)