What we're saying here is that someone offered to let the blog owner post some well written and original content on their blog, that would be relevant to their readership and mutually benefiting to both parties. But that's bad because Google says so.
Now, if the content is bad, or not relevant to the readership, or overly spammy, then the blog's readership will presumably react. So it's up to the blog owner to protect their reputation and vet all content that they publish. But assuming the content is good, haven't we just got to a nice place? With marketers realising that the best way to promote their product is to persuade respected content publishers to endorse their products and by making content that people want to read?