Is this really that much of a problem? I mean, look at Caramelldansen. Very few people seem to know the original anime the original video was from, but is that any reason to blame Caramell or the creator of the video? Or how about Buri Hamachi. How many people who know about that meme honestly know it originally started with a song and character from Ar Tonelico? Being mad at the creator for making a fan work of what they like seems counter productive to me. I don't see any reason for people to get mad at those who see videos without knowing what series it's from either, though. It's not like all the world is required to experience the full Touhou universe simply because they enjoyed a IOSYS PV.
You took my comment at face value.
However, I'll admit that when I fail to take a topic seriously, I tend to post a sarcastic comment that more or less matches my thoughts on the subject.
Anyway, here's a little more serious comment for the interested.
The thread isn't much, but there is some attempt to define what a Touhou fan is exactly.
I guess the problem with fan-dumb, Touhoufags, etc. is you get the gamers of the original series versus the people who just stick with the fan content, with things like music and PV's getting the most attention. (A lot of them lurk Youtube and the sort, but don't decide to join a forum such as this... not even to ask "Where does I download Touhou gaem")
In other words, for some people, it frustrates them to know that a series they love is getting attention for all the "bad" reasons, and that causes bad reputation for the fans of that series. Something like that, I guess.
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http://www.shrinemaiden.org/forum/index.php?topic=5459.30 Eh. It's late and I just got back from doing a few errands. Tired... Someone stretch this topic a bit.
If you check that thread, I loosely comment on how Touhou fans are ONLY those who play games. Many other people feel this way of course, but some of them take it personal and then we get this hatate, err hate.