Unfortunately, credibility does need to be earned, ideas do not exist in a vacuum, nor should they. This is a necessary adaptation to the quantity of information presented to us in the modern day, every day. This is why pure rhetoric and rationality cannot be used to understand the world around us, it's simply impractical to do that much processing every day.

Calling a person's credibility into question is thus very valid, as it implies debate is not being entered into in good faith. If you wish this resolved, you will have to earn your right to be listened to by anyone who has any significant amount of experience with online communities. It's just too easy to spout fancy sounding bullshit like some kind of firehose, manufacture evidence in a variety of ways, and just generally waste people's time. It happens all the time.