@MelanieShebel It is possible to blacklist a tag, such that it cannot be added any more to new questions. For example, try asking a new question and tagging it with
chemistry; when you try to submit the question, the system will tell you that it is not possible. However, we need to clean up the existing uses of the tag (or at least commit to doing so - considering the sheer number of them) before we can get it blacklisted.