I don't see how google can punish anyone for excessive links (1 way), if this was the case all you need to do is order a few submissions for your competitor, submit them on the worse link farms etc, and thats it now, they are hated and de-indexed. Therefore how can you be punished for having links (1 way), different story if you are linking back to sh*te, then you are in trouble.
Because google search results should return relevant information that is based on a sites natural reputation. When people use spam bots to build page rank, those are not natural links. In fact, its cheating. So google issues a penalty when website owners do something that might affect a sites ranking in the results pages.
The question is how do you avoid duplicated content on a blog, when you have tags, categories, month, etc... every widget repeating the content... On a blog, a single post is duplicated in all those tags and widgets. Even in main (index.php) and in single.php.
blackhat is an art.. if you master in black arts you don't get penalized.. but if you don't know what you are doing you will get penalized.. so it is not right to make generalizations.. I know many people doing blackhat seo for many years and never get penalized...
You get penalized because you have duplicate content, Buying and selling of links, link farms, spamming, etc..
Link farms is still not a complete black and white there various types and sometime google is not able to catch farms
Btw can be consideration form used as well for site which are penalized(it says its for sites banned from index)