[reboog711]

Ignoring any ethical concerns you may have...

Advertising has often been comparing yourself to other brands. As one real world example: The Pepsi Challenge from the 80s. People drank Coke and Pepsi blindly and chose which one they liked better.

It is not illegal in the US and not inherently a misuse of trademark law. I'd be surprised if you were to tell me that Uber and Lyft are not buying ads against each other's search terms.

[chatmasta]

Google does not allow bidding on trademark terms you do not own, so there is at least clear precedent.

Edit: Oops, mostly wrong. Guess I've had an adblocker for too long. :)

[jasongill]

Yes they do, and they have for 15+ years. Their website even says:

Trademarks as keywords Google won't investigate or restrict the selection of trademarks as keywords, even if we receive a trademark complaint.

Search for "Uber" on Google and you should see a Lyft ad right near the top of the paid section.

[tyingq]

Worth noting they will police the use of the trademarked term in the ad itself. But only after the trademark owner complains about it, and not in all situations. You can still bid on the term, of course, just somewhat restricted in what the resulting ad can say.