First, for the specific question I think a main problem was really that it was easy to understand it not as the question of a mathematician asking about how to understand or deal with stereotypes they might face, but rather as willful provocation of an "outsider". And, I think this is what happened to some extent and explains the very negative reaction you experienced.

Second, the above being said, even without this misunderstanding it could well have happened that the question is closed. If you want to make sure you never face a problem with closure or negative reactions to one of your questions, I think 'the red line' is a considerably before you even arrive at any type of such questions.

The only questions that are really "safe" are specific research-level question in mathematics (provided with context and motivation), everything else could by considered as off-topic by somebody.

This does however not mean that you must limit yourself to these types of questions, but only that you should not be surprised to face some opposition if you ask other types of questions, but might well also find some support. And then the final outcome ca be either way. There are no clear rules.

What you should try to avoid is causing the impression of trying to be provocative or just trying to stir-up some discussion or promote a point of view, as opposed to asking an honest question in answers to which you have some actucal interest. It can also help to point out why and how having answers to the question would be helpful to you, as opposed to leaving the impression this is just asked as it is sunday, the weather is bad, and there is nothing interesting on TV or somethin along these lines.

I am quite sure there was once a question a long the lines "How do you reply to somebody saying ''I was always bad at math'?" But cannot find it momentarily. This worked then for some time, but standards got rather stricter regarding this over time so it might not work now. But also it might.

I think there also was once a question fairly close to what you asked, which also did not work then. And, we had all kinds of things 'Mathematics and marhiuana', 'Mathematics and pacifism',... Essentially all closed. Though the two mentioned also suffered the problem that some did not perceive then has 'open' questions, but rather as promoting some opinion.

A final point: the tag math-psychology, on the one hand seems to be used for quite different things, rather psychology of learning and communicating math then the psychology of mathematcians, and also there being a tag for something does not mean much at all; it merely means at some point in time some user with 250+ points (so you for example) thought there should be such a tag and used it (and it is still used somewhere, ie, the question did not get deleted or the tag changed). So, please do not infer from there being a tag for something it is alright to ask about it (for example, there is a tag 'latex' but meanwhile most any question on latex is considered off-topic among other things as there is a Q&A site for it specifically).

You shoudl also wait for other input. I think many think I am very strict regarding MO; this would IMO not be quite true yet then it is likely true that my opinion on MO are rather to the puristic end then the open of the spectrum of opinions.

Also, if you eventually decide to reask something like this, you should definitely not do this too soon. Reasking something that just got closed is considered against etiquette. So you should avoid causing this impression.

Added: written before seeing any other response, but it seems still relevant.

Regarding François G. Dorais's question on deleting the tag: I am not just not against it I am actively in favor of deleting it.