I would say that is unethical. If s/he really wanted information from a forum, then s/he could always ask the forum moderator for permission to post questions. Whenever you do psych experiments, you HAVE to get permission from the participant (even if the experiment itself has some manipulation) and a lot of times participants are rewarded for their time, so it's definitely a rip-off on the participants' parts.
Also, how would the psychologist even be able to publish this kind of work? Most research studies are conducted from grants (which come from universities/hospitals/government), and in published studies one has has to explain how s/he ran the experiment, the actual results, cite the references, etc. How would this psychologist even be able to publish such "research"? I'm pretty sure scientific journals would be smart enough to reject "research" based on internet browsing and fully manipulating people.
I just don't understand how a psychologist would be able to publish the research in the first place; it would be just as unethical (if not more) if a reputable journal actually published something like this. Even as an undergraduate, when my professors explain experiments in lecture, they cite the researchers; and when I have to write research papers, we can only use original articles from approved journals.