Wait, what?
How is it not categorized, when you assign one item to multiple? It is clearly categorized. When the item is described with "computer" and "games", under both you will find it. As from a user's view, it is highly logical. Let's say I am looking for an item about "computers". Where do I go? Under computer category. The same about "games". It doesn't change the approach in any kind of way. But it doubles the chance to find that item.
But now, let's say my item is best described under both categories but I can only list under one. Now, the user, who looks under "computer" will find the entry/item. But the user who looks under "games" won't find it, cause it is not listed there. So he will think "oh, there is no entry for it". So he will miss completely that item, even though the item would have been sth for him.
It is highly illogical to expect that users must find the exact right category they are looking for. How the hell is that one user supposed to know that this one item he is looking for is under "computer" and not under "games", whereas he is interested in games and not computer???
By allowing only 1 category per item, you are excluding all the people who looked under the "wrong" one. This is exactly the reason why forums die. The search system is abysmal. With this kind of attitude, forcing people to search for the exact keyword (or in our case the exact category), makes everything so hard to find and it needs luck to find the correct one. People can't be bothered with this stuff. It must be quick and easy.
The folder structure on my computer is solely based on my personal preference. That's why it works, cause I alone decide where to put an item in which folder. But let me invite you to my room and use my pc. I'll give you the task to find something on my pc. I bet you won't find it, cause you will look under the wrong folders, cause you will expect some items under different folders. You can't possible know my categorization of folders. Let's say I have a movie made in the 90s, genre crime and in full hd. In which folder you will look? Under 90s? Crime? full hd? I know where I put that movie, but u don't know it. And this is exactly the same situation here with this add-on (or any other similar add-on with this bad architecture). The guy who put the item under that 1 category knows where to find it. But all the visitors who visit that page don't. So, you expect them to find it?
Tags are useless. I don't want to explain why, simply said, it is a superficial categorization which only makes the situation worse, than better.
"Make it more general": nice. So why I do need categories, when I have to make it so "general"? What is the point of categories then?