I don't think the people who blindly defend Google have an understanding of what Google is doing with its search results. Let me give you my experience as a site owner.
I run a popular sports website. On April 24 2012, I saw a 30% decrease in traffic. I figured that maybe interest in my sport had cooled off because the season was winding down, or that it was a temporary situation. But the traffic didn't get any better. But then I noticed when searching Google that my site wasn't coming up as often as it used to. In fact, when searching for topics that were only covered on my site, my site wasn't being returned in Google. If I went to Bing, they came up right at the top, but Google searchers were left thinking that no such information existed on the internet.
I learned that on April 24, Google put in an algorithm that penalized websites for "webspam". What is webspam? They identified it very vaguely, but the examples they gave were egregious - people who put thousands of unrelated words on a page, or people who were running massive link exchanges designed to boost other websites' popularity in Google's results. But my site did none of that - yet Google cut it from appearing in the search results by about 70%.
Do you know what recourse I had as a site owner? Zero. Google doesn't have a customer service department. They have an online forum staffed by volunteers who are, quite honestly, arrogant and abusive. Occasionally an actual Google employee drops in, but they won't answer questions because they don't want people to be able to figure out their algorithms.
My story has a happy ending because last week, my penalty was lifted. No explanation, no communication, it was just something I noticed. Many others have not recovered, and there is always the threat of having the penalty applied again. To be clear, this penalty is applied by an algorithm, not by a human. There is no human ability to override it. That's just wrong, and scary too.
Some have speculated that Google's algorithm penalized sites in order to force them to purchase advertising on Google. Imagine that you're making $500 a day from your #1 Google spot. No need to advertise. But if Google demotes you, then maybe you'd spend $250 per day to get back to the #1 spot? It's speculation, but well-reasoned - before I learned that I was demoted by a penalty, I increased my advertising with Google to try and get traffic back. Google's advertising profits went up after they put this penalty in place.
Another reason that Google gives for penalizing sites is if they have "too much advertising". So they want sites to remove advertising. That itself is an antitrust problem - because less advertising on sites means more demand for Google advertising.
Google also penalizes websites that run affiliate programs that Google doesn't find "add much value". Let's say that you have a site that reviews books, and in your review you provide an Amazon link so that if someone buys the book, you get a commission. Google doesn't like that. They want to send the user to Amazon instead. They want to cut out the middleman.
Google may also be (or may soon be) penalizing or rewarding sites that don't mark up their data in a way that Google can interpret with an algorithm. But since Google has expressed an interest in cutting out the middleman - websites - when it comes to returning information, this could be an attempt to force sites to train their own replacement. They're already doing this - they pull data from Wikipedia (which Wikipedia editors have manually scraped from other websites) and display it right on Google's page. No need to leave Google for your information.
By applying penalties, Google has become like a credit bureau. Last I checked, credit bureaus were regulated in the USA because they have the power to do significant damage to people via things like errors and omissions. Credit bureaus have to give you a chance to correct your credit rating, to fix errors, and they have to give you a general idea as to what factors they use to rate you (Google allegedly uses 200 factors, but won't disclose them).
Google is a de facto monopoly. A website can't afford to ignore them. They should be investigated and there should be lines that they cannot cross because crossing them would be anti-competitive.