For me, if I read a paper that discusses work that is my area of expertise and that discussion is simply incorrect, I doubt the credibility of the rest of the paper, and the editorial process of that journal.
I am seeing this happen more and more. It is most prevalent in open access journals. Though some are high quality, some are not. It is clear that papers are not reviewed correctly or the authors don't understand the science (also increasingly evident at prestigious conferences). This worries me greatly since these poor quality papers are now being cited in papers in highly respected journals. As time goes by, the errors in the original papers become seen as correct.
Sadly, the damage is done. I used to consider peer-reviewed papers as authoritative but now I am skeptical. Science shouldn't be that way.
Open access is a commendable concept but it is already contaminated by poor content. I fear for the future of peer-reviewed scientific knowledge sharing.