This was meant to be some kind of humor of course, and I was stereotyping the categories. Anyway, there's still a bit of truth in that if you bring each type of fan to the extreme, which is quite frequent if you think about Twitter (mostly) or even Facebook sometimes.
Anyway, a "casual fan" (and I didn't make that word up) is a type of fan who almost-regularly watches the show on tv, but doesn't really pay attention to everything, doesn't know the actors (aside maybe from the main two), makes spelling mistakes when writing the names etc. It's basically at least the 60 per cent of a live audience. Hart used to talk so much about this type of fans. They are maybe also the luckiest, because they just enjoy the show and never get involved in the fandom drama. On the other hand, sometimes this type of fans are really annoying because they end up complaining about stuff which is not worth of complaining.
(when is Parker coming back? and Parker just got back with a new face and they didn't even notice! eheheheh)
About the "I only like one character", I don't have anything against people who love a show only for an aspect of it, or just an actor or a character. It's always just all about how you handle it. For example, this website (and your account on Twitter), is about TJ and people on here mostly discuss the aspects of the show related to Hodgins, Angela and Hodgins or TJ's other work. This is a positive example of being a fan specifically of something/someone, because what happens here is mostly creating a cool/happy/relaxed enviroment about something a group of people love. This is not bad at all. But this type of fan becomes bad when for example, they only love Tamara Taylor (this is random) and instead of praising Tamara/Cam, spend their time hating on the show and the rest of the cast. And with hating I mean hating. Like sending tweets to the people they despise.
This is different from disliking an actor from the cast, or a storyline, or a couple of other characters and discuss the reasons why you do so. I mean, everybody is allowed to watch a show for whatever reasons, but I don't get why people really love to spread hate instead of praysing what they love.
For me it's different, I am a weird type of person. I can't have a favourite show if I hate more than 1 main character on it or there's just too many things that I hate. Of course I have my favourites (and that's right), but in order to get hooked on something I really need to like that product as an ensable or otherwise I just can't keep watching just for one thing.
For Bones it's different, because now I have quite a few things I don't like anymore (although I do love some other things), but I always think about how long this show has been on. When I started to watch it tho, I basically liked the 90% of what I saw. This doesn't mean there weren't characters or annoying storylines (I am of the idea there's no perfect tv product), but anyway the good things about the show - or better, the things *I* found good- were always the majority for me.
The Zack storyline, I don't know how much time has passed since you started watching the show, but when I started it was 2009 and s4 had just ended, so back then I wasn't still involved in the fandom or read opinions online and i liked that storyline. I mean, again, I know it wasn't done exceptionally and I was aware of the 2008 writers' strike, so that plus the fact that s3 is still my second favourite season and the fact that I liked the interns right away, I didn't have anything against how it was handled. Plus, Eric had his own personal problems and I was okay with him not being on the show anymore. I mean, I am a bit bitter about no one knowing Zack was innocent, but again, it's been so long. It's one of the things you either resolve right away or loses its meaning. Also, my main reason for liking Zack were his interactions with Hodgins, but I have to admit I came to like some of the interns more than him. Maybe that's why I am fine with it.
Anyway, even here my theory still holds: it's how you handle things. If you liked Zack and you want him to come back it's fine, but asking about it over and over again in a rude way, that's what annoys me.
Last point.. Stopping to watch a show is perfectly fine, just as fine is to come back after quite some time (I was never able to do that with Bones, but I basically do that everytime with every other show I watch.) it's the complaining that I don't get. I mean, if someone stops watching a show in s6, how can you complain about a s8 storyline without having even watched it? I've always found this kinda stupid, but maybe it's just me. Lol. One thing is to say "I stopped watching and I think I wouldn't like this storyline" but this is different from saying "It sucks."
I kinda stopped watching Grey's Anatomy years ago, and whenever I read headlines about the newest seasons I have opinions of course, but I would never click on them just to bash a show I am not even watching anymore. That is all.