I tend to disagree with simply using a monolithic airspace tag. I think using that tag would be appropriate when a question encompasses multiple types of airspace, but many questions are going to be asking specifically about one, and it seems appropriate to tag them as such. Blanket tags which cover tons of questions are the less useful as a search filter.
We should remember there are more types of airspace than just the classes. There's also MOA's, warning, restricted, prohibited, temporary restrictions, ADIZ, TRSA, voluntary restrictions like wildlife refuges and nuclear power plants, and more. All of those technically would fit under airspace, but it wouldn't be very useful.
Even if airspace was limited to implying airspace Classes A-G, I also disagree that people would be equally likely to be experts in each of the airspace classes. A pilot here in the Northeastern US might have a lot of advice for navigating through and around Class B, whereas a pilot in Alaska might have a lot of practical knowledge about operating in uncontrolled Class G. Imagine you've never flown through a Class B, and you want to do a search for all questions tagged class-b before your trip to see if any questions stand out, which you hadn't considered before.
If nothing else, since operating rules in the various airspaces are different, I feel they warrant unique tags.