You don't need to know how something was built in order to critique the experience of using it. A non designer is not going to be good at identifying solutions

You don't need to know how something was built in order to critique the experience of using it. A non designer is not going to be good at identifying solutions to problems because that does require knowledge about how the sausage is made, but they should certainly be listened to when identifying problems. Not doing so would be madness. (Not to mention a lot of the commenters on here that you're decrying as "non designers" probably do have experience with design, considering the userbase of HN)