I don't think we should. Example: https://ethereum.stackexchange.com/questions/tagged/metamask
I agree with @mids "generally speaking; if we allow questions about specific dapps, it makes sense to me that we also allow them to be tagged as such."
So we can make this be dependent on Are questions on specific DAPPs on or off topic? ?
In this specific case I would reason that
metamask is more than a "regular" dApp, it is "mist for your webbrowser". If we allow
mist as tag (https://ethereum.stackexchange.com/questions/tagged/mist), I would also allow other wallet/browsers.
More generally speaking; if we allow questions about specific dapps, it makes sense to me that we also allow them to be tagged as such.
I agree with you. In general, a tag that only applies to one question shouldn't be a tag. This would apply to questions about a specific, relatively unknown Dapp. It doesn't make sense to make a tag for every single one, but it might make sense to make one for common/popular Dapps, especially ones that effectively act as libraries.