I agree with you on this one totally.
I started Open Mic for example and since it started getting more popular some people are using that tag even when it has nothing to do with music. I don't mind sifting through it and understand people are trying to get some exposure, but when it's not related to the tag in any way it's a bit frustrating to open a post to discover it's not related.
We do need categories that offer people shorter posts. Most of the people online are not content creators. That's just a fact. If we want mass adoption we'll have to come to terms with that and find a way to cater to the content consumers and sharerers.