To actually address the point of the thread.
I don't necessarily think that Sheik is a man.
But I do find it a bit frustrating that the "Sheik is Zelda therefore Sheik is a woman" is completely freaking ignoring the actual question.
Think about it this way. Sheik, within the world of Zelda, is a fictional character created by Zelda herself. Zelda then, disguises herself as this character. The question is not "Should we consider Zelda a man when she's disguised as Sheik for some moronic reason?", the question is "What is the gender of the character Zelda invented?", and in that question, the gender of the person wearing that disguise is in fact completely irrelevant.
To put it in perspective, let's do the same question with a different feature, like eye color.
What's Sheik's eye color?
I'm pretty sure everyone would agree they're red (unless you wanna be a smartass and bring up a specific shade).
When you use the "But Sheik is Zelda" thing with the gender question, it feels exactly as if you were saying "Zelda's eyes are blue and Sheik is Zelda, therefore Sheik's eyes are blue" in this scenario. The question is not about the real person behind the disguise, but the disguise itself. In this case we're not looking for Zelda's true eye color, but the eyes that was given to the fictional character of Sheik. Just like we're not looking for Zelda's true gender, but the gender that was given to this fictional character. Maybe the intended gender was female. Maybe the intended gender was male. But when even official sources say "what the **** are you asking Sheik is Zelda you dummy", it becomes impossible to find out.