To be clear, and there's some nuance here, labels aren't in and of themselves forbidden. Rather, it's when those labels are used in a negative way.
In essence, if somebody is using "tanker" as a means of describing a philosophy that thousands of fans fall into, that's not necessarily against the rules, so long as it's not used derisively. In the "who are tankers mad at?" thread, nobody was called out, and I thought it was a pretty respectful thread trying to ask a discussion-worthy question.
The "are you anti-tankers happy now" thread wasn't really within our rules, because as you said, it seemed as though it was created specifically to call out folks, and didn't seem interested in a discussion; it seemed more dismissive and sarcastic than necessary. Reasonable minds can probably disagree on that, though, and I don't really see anything wrong with "Anti-Tankers"; it would be different if it was "Green Teamers", or something. However, even under my interpretation, I didn't see it until it was 5 or 6 pages in, and most of the responses have been civil and even proud, so it wasn't locked. The thread may violate our rules, though, and if I had caught it early it probably would have been locked.