It is true that you will most likely not be penalized for these pages, Google is pretty good at figuring out common canonicalization problems in my opinion and would most likely not penalize you for having duplicate content. I would encourage you to dig a little deeper and see what additional problems these pages could create though.
Consider that Google will waste valuable crawl bandwidth crawling these meaningless pages, rather than focusing on the important content you want them too. If Google is crawling them, you can most likely bet that PageRank is flowing through these pages as well, diluting the link equity of your site.
Are you using Wordpress? There are a lot of great plug ins that can help you manage these pages. You could control how Google crawls these pages with your robots.txt, by placing meta robots tags on the pages using a plug in, or by placing rel=canonical tags on the pages pointing back to the page that is the original source.