I don't really read non-fiction books for leisure. For school, maybe. But not on my own time. If I want to enjoy reading, I'll read fiction.
Plagiarism is a big issue when it comes to blogging. Annabelle from Sparkles and Lightning was a victim of plagiarism. The bottom line about plagiarism is that it is WRONG. There is no correct instance to plagiarize. From my first years of learning/schooling, we were taught not to copy/cheat/plagiarize. The lesson is the same no matter what age, no matter what job, no matter what person.
Also, do your research and find out the facts if you're not sure about something. Don't just go putting some rude remark about something error you saw in a book, only to find out that you were wrong, and there is no inconsistency. Do a fact-check if you're not sure if something is supposed to be that way or not. I suppose this really affects historical fiction novels, but any genre as well.