That's absurd. Google's not going to see the filtered reviews unless they start doing a lot more JavaScript execution than they've been doing, and why would Yelp care if a browser extension or spammers see filtered reviews?
Google's not going to see them because they have purposefully made them difficult to scrape...
I'd imagine Yelp would rather not have a "Yelp Unfiltered" extension made and their filtering becomes less important. Same for helping spammers automate their processes by checking up on their reviews.
It's a race to the bottom though, the spammers will eventually win.
