You'd probably get the same question from a plumber if you asked him how to plug a pipe in a non-intuitive way. He has no way to know your pipes are laid out in a strange way, and the only spot you have left to add said junction without redoing your plumbing is back there - unless you tell him.
Sure, some people are assholes, but that's just people. Nobody's in your mind, they can't guess your requirements, thought process and level of experience. In my experience, more often than not, asking the question "why would you want to do that?" gets you a bad reason. "I did X this way because Y. I need Z." would filter the legitimate questioning out. From there, the others are just assholes, and those are everywhere.
In my experience, "why would you want to do that" is dismissive, defensive gatekeeping, typically used to imply that the questioner is an idiot, whereas "why do you want to do that" extracts a reason, bad or not, that can be worked with.
I'm fairly active on the Python slack channel, and this very question comes up really often when people ask for help, and in my experience, is basically never meant as disrespectful.
As for the small differences in semantics, I'm not a native speaker, neither have outright negative connotations to me, but I feel like getting tripped up on such a small thing - and simultaneously assuming the interlocutor's intentions - is kind of overblown.
The semantic difference is not small. "Would", using the subjunctive, implies that the "want" is theoretical, that the person asking is in some sense trying to come up with a hypothetical situation that can be written off as being unrealistic or a silly edge case. Using it diminishes the experience of the questioner and is intrinsically disrespectful. The fact that people have got used to hearing it so much that they use it without questioning how rude and unwelcoming it is says more about that community than about the grammar.
"Do", in the present tense, does not carry those connotations. It implies "I have acknowledged that your want is present and real, but I need more information about your context to be able to help."
> You'd probably get the same question from a plumber if you asked him how to plug a pipe in a non-intuitive way. He has no way to know your pipes are laid out in a strange way, and the only spot you have left to add said junction without redoing your plumbing is back there - unless you tell him.
Sure, but if I told a plumber they'd understand and help me find a solution to my problem. That isn't what happens on StackOverflow, instead they try to convince you that you have to change your problem to fit the solutions they're familiar with.
Sure, some people are assholes, but that's just people. Nobody's in your mind, they can't guess your requirements, thought process and level of experience. In my experience, more often than not, asking the question "why would you want to do that?" gets you a bad reason. "I did X this way because Y. I need Z." would filter the legitimate questioning out. From there, the others are just assholes, and those are everywhere.