Since you posted this here, I might as well throw in some sense and take some time to write you out a lengthy response. I know that the people on the wiki influenced your decision much, and I do apologize. I hope you will consider coming back. But as for the rest:
I first want to note that I am terribly, truly thankful that an Arthur fandom is not accepted. Muppet fandoms are the same way...usually not accepted by most people, as it is regarded as kiddie entertainment. But in my mind, that's the thing I love about fandoms. It's the fact that they go against society, against what is "popular." It's the thing that, in fact, drives me forward to be a fan of something. The fact that Muppet fandoms are not accepted is what allows me to talk endlessly about the Muppets to everyone I know. I have something DIFFERENT about my preferences that makes me stand out, and that's what I love. I live for the moments when I can sit back and realize that by being a fan of something unusual, I not only stand out, but I also get the last laugh in the end, because they do not know what they were missing.
To be honest, I would really hate it if the Arthur fandom was super mainstream. I would hate it if the Muppet fandom was super mainstream. Sure, I love it when new fans come about, but to have a fandom to the extent of the "popular" things nowadays, I couldn't stand that. Because it doesn't make me stand out in a weird and strange way.
I have to say something that I believe I've said to you before: IT AIN'T ALL ABOUT MARC BROWN. Sure, he plays a part in the show's development, but to be honest, I don't think he even really works on it to that much extent any more. Sure, he could most likely pull it off the air with one word, but there are other people involved in the decisions.
Honestly, the problem is not that Marc Brown doesn't care. It is that he doesn't know. I'll betcha a hundred bucks that if you asked Marc Brown, he would honestly have never heard that fans aren't liking the show much anymore. Remember, he isn't very technology savvy, so the only concerns he would really catch wind of would be through letters (and who writes those anymore?) and of course contact from other employees. You say that he isn't caring, but the problem really is that the complaining fans keep talking to a brick wall.
Vandalizing the wiki is not caused by hate for the Arthur series. Not at all. It is because Arthur is regarded as a baby show by many people. People watched it when they were little, so now it is fun for them to vandalize a wiki about the "old baby show they used to watch." It's enjoyable for them. Family Guy Wiki, for example, has less vandals because it is not regarded as a baby show. People like the show in their current age rather than former, and don't have a will to vandalize it.