Employees shouldn't be blogging on company time (except on a company blog, where the IP issues are unambiguous). I don't think it's unethical, because most companies no longer seriously invest in employees' career advancement, so employees have to sneak away time for that, and everyone successful "steals" a lot of education. I do think it's sloppy and reckless to perform side work
you actually intend to use on company time. If you are going to go ahead and do it, at least show you're not a total fucking moron by turning off timestamps.
I understand that it's annoying if you suspect someone's "wasting company time", but I the larger issue that people have with this is mostly irrespective of whether the blogging happens during work hours, especially as those become increasingly vague in definition. The issue, for the Baby Boomer clientele of WSJ, is that it punctures the illusion that people are supposed to keep that they're 100% dedicated to the corporate goals and working as hard as they can. (If you have side projects, even if they occur outside of work, they will decrease short-term work performance from a manager's perspective. If you work 80 hours per week in total and give your boss 40, what you're actually giving is worth 25-30, tops, because of the per-hour productivity slide.)
Baby Boomers had to put forward an image of total loyalty: no side projects, no interest in independent credibility, happy to work on whatever they were assigned to do. Millennials don't buy into that, not in the least. They put their careers ahead of management's objectives and it shows, and it's making a lot of people angry, but it's a rational response to a new economic reality.