To restate what several have already pointed out:
Anonymous IS an identiy. However, it is submitting to a mass identity rather than an individual. Entering a relatively unique label (with tripcode) in the name field only helps to make you slightly more traceable, doesn't make you a good poster or bad. I sometimes use more identifiable labels than Anonymous, I sometimes use labels (usually different depending on what board it is).
As I see it, to once again restate what so many already have stated, people need to stop whining and learn to deal with it. What's with the massive discrimination towards ID-people, denying them rights to behave like Anonymous does? I don't mind idiots using a name/tripcode, makes it easier to semi-skip their posts (I usually still skim through a piece of the text - who knows, they might actually produce something interesting for once).
I usually read every single post, unless someone's being an idiot and helps me to ignore his posts by IDing himself. I also never refer to people by their name but by post number, regardless of if they're Anonymous or not.
I've seen many cases where people who consider their main identity to be Anonymous temporarily take on a name+tripcode just to flame and cause aggravations. Vice versa too.
People need to drop the Holier-Than-Thou attitudes.
People complain about that Anonymous is a jerk and an asshole? Prove them wrong! Show that everybody isn't like that.
People complain about that IDtripfags are being jerks and assholes?
Take on a name+trip and become a good role-model! Show that everybody isn't like that.
Personally, whether I tripfag or not depends on what I wish to accomplish with the post. If I just simply want to tank some random person for uploading a really neat torrent, I post anonymously. If I in a thread want to post a more serious reply that probably will need to be identiable so that one won't have to refer to all ones previous posts if someone demands lengthier clarifications, or put up a longer and more elaborate version that the majority of people will go tl;dr at because they can't be arsed to re-read it and find the changes - I use a name.
I maybe should mention as well that I frequently post to 2ch as a tripfag, though probably 40% of all my posts there are anonymous. If it's a short irrelevant post: Anonymous.
If it's a lengthier post with something more important: ID.
If it's a lengthier post with something standalone: Anonymous.
Etc.
I never have had any real problems with people whining at me being a tripfag at 2ch, when I have been doing so. Giving some of my posts an identifiable label helps people sort the content quicker, to give them a quick idea of along what line the post will be. My 2ch label never got flamed, not even when I argued against lolicons. People usually see that label-identity as a producer of logical and sensible posts, who is willing to seriously listen to other people's arguments. Should they trust those posts more than Anonymous? No, not unless they have good reasons for believing otherwise. Which some people do. But only some.
Soon time to hit submit; What category does this post fall under (appart from the obvious tl;dr one)? Anonymous or tripfag?
Is this post irrelevant? No.
Is this post something that I am likely to build on, if I am to ever post again? No.
Anonymous it is, then.
Use your brains, people. There will always be idiots, trolls and assholes. I don't see why people feel it's so much easier to forgive them if they're being anonymous. Treat post equally, except for when it makes your life easier/better to not to - in the cases of where you have the upper hand (i.e. either know the Anonymous poster or the tripfag and thus being able to better tailor your reply/post to the person).
(wow.. this post is probably the longest one I've written for half a year or something. ah well. tl;dr! Cheers!)