In my experience doing user interviews, I find other professionals wanting to charge for knowledge or gate keep them in general. Don't get me wrong, you should charge for knowledge, but some knowledge shouldn't be charged for. If I'm asking you what challenges you face at work and I expect your response to be asynchronous, I do not have to necessarily pay. If I need to schedule a call with you and take more of your time, that's a different story.
My experience;, say you post on a sub for non techies, a few users will get angry and come at you with "here comes another techie who thinks he can change the world, pay people for their time" or something similar. In contrast, you can posts an issue you're having on Stack overflow and have it resolved by a random stranger who's happy with a thank you and an upvote.
This culture doesn't exist anywhere else, even in academia.
Thoughts?