Harshness is not the problem, credibility is. I don't mean that you sound like you're lying, but that it's impossible for anyone to evaluate your assertion or how it applies to their use case. Anyone who reads your comment (including me) just files it away in their head as "somebody on HN made an unsubstantiated comment that Julia sucks in production in some vague way".

If I were in the position of making or advising someone making the decision of whether or not to use Julia, an unsubstantiated, untestable assertion like that makes virtually no difference in my decision or advice. I hope it's clear this is not an insult, it's just that if I have no way to evaluate your assertion or its applicability, there's no way for me to incorporate it into my decision or advice.

By contrast, if you could point to even one concrete example, I could file it away in my head as "someone on HN pointed out that Julia has X, Y, and Z problem". If I were in a position of making or advising a decision on Julia, I would be able to evaluate whether it applies the use case in question, whether it points to some deeper design problems with Julia, or whether I even think it's a problem at all.