What was aggressive was the blunt and forceful way you issued the correction and then followed it with a snarky and personal question that was not really a question.

Some things you could have done instead which would have been less aggressive: (1) check whether "maths" vs. "math" is actually an error (e.g. like this: https://www.google.com/search?q=maths+vs+math&oq=maths+vs+ma...), (2) ask the other person why they said "maths" rather than "math", (3) bring up the analogy to "economics" in a curious way rather than as a hammer.

The fact that your correction was wrong (in the sense that the other person's spelling was perfectly correct British English) is actually beside the point here, because even if you had been right, the GP comment would not have been a good way to express it.

Re the Milner quote: I'm glad you noticed it! It is an endlessly fascinating and profound statement, and every time I happen to notice that it's in my HN profile I'm glad I put it there.

Don't forget, though, that of the two important words there (toleration and conflict), it is toleration (not conflict) which has first place. The question is what it means to tolerate conflict rather than denying or trying to exclude it.