I agree. It's definitely in no way similar to the US justice system where you're assumed innocent until proven guilty. Copyright infringement is illegal. As such it should be decided by a court of law.
A "valid" DMCA takedown request doesn't necessarily mean that the person submitting it has been determined to BE the real copyright holder or to BE infringed upon. It simply means you submitted all of the information required on the form. And by Google's own admission, they take down approximately 97% of all contested content submitted via DMCAs.
This is essentially saying that, "If you have a DMCA takedown request submitted against your site then you are assumed to be GUILTY of infringement." Most hosting providers will automatically take it down JUST to avoid getting caught in the middle of any legal dispute.
I don't have a problem with DMCAs. I've used them myself against people who have scraped my content. But using them as a ranking factor when the tendency of hosting providers is to takedown the content as the result of almost any DMCA request first... and hope the accused doesn't ask questions later... is very dangerous and VERY open to manipulation. Hello Roboform and other tools... You can definitely automate submission of "valid" DMCA requests.
And now with Penguin, people are actually submitting DMCAs as a way to get links taken down. They are claiming that other sites merely mentioning their company domain name and/or linking to their site is a copyright infringement.
And then there are those sites that used article submission to generate back links and are now being filtered by Penguin. Many are filing DMCA requests against every site that republished their articles even though those sites had the right to republish them (the author accepted that as part of the submission site's TOS/T&Cs.) These re-publishing sites are not violating any copyright law because the author specifically gave them permission to do so.
IMO it's a very bad idea to use this as a ranking signal when the standard response to a DMCA request in the industry is to take down content first, and then expects the accused to prove their innocence later.
But then this is all about the billions of dollars Google stands to make from the entertainment industry and other special interest groups that they bowed down to resulting in this change... It's not really about improving the SERPs.